D (programming language)

The D language reference describes it as follows:

D is a general-purpose systems programming language with a C-like syntax that compiles to native code. It is statically typed and supports both automatic (garbage collected) and manual memory management. D programs are structured as modules that can be compiled separately and linked with external libraries to create native libraries or executables.

Features

D is not source-compatible with C and C++ source code in general. However, any code that is legal in both C/C++ and D should behave in the same way.

Like C++, D has closures, anonymous functions, compile-time function execution, design by contract, ranges, built-in container iteration concepts, and type inference. D's declaration, statement and expression syntaxes also closely match those of C++.

Unlike C++, D also implements garbage collection, first-class arrays (std::array in C++ are technically not first-class), array slicing, nested functions and lazy evaluation. D uses Java-style single inheritance with interfaces and mixins rather than C++-style multiple inheritance.

D is a systems programming language. Like C++, and unlike application languages such as Java and C#, D supports low-level programming, including inline assembler. Inline assembler allows programmers to enter machine-specific assembly code within standard D code. System programmers use this method to access the low-level features of the processor that are needed to run programs that interface directly with the underlying hardware, such as operating systems and device drivers. Low-level programming is also used to write higher performance code than would be produced by a compiler.

D supports function overloading and operator overloading. Symbols (functions, variables, classes) can be declared in any order; forward declarations are not needed.

In D, text character strings are arrays of characters, and arrays in D are bounds-checked. D has first-class types for complex and imaginary numbers.

Programming paradigms

D supports five main programming paradigms:

• Concurrent (actor model)
• Object-oriented
• Imperative
• Functional
• Metaprogramming

Imperative

Imperative programming in D is almost identical to that in C. Functions, data, statements, declarations and expressions work just as they do in C, and the C runtime library may be accessed directly. However, unlike C, D's foreach loop construct allows looping over a collection. D also allows nested functions, which are functions that are declared inside another function, and which may access the enclosing function's local variables.

<span id="mwlQ"></span><span class="k" id="mwlg">import</span><span class="w" id="mwlw"> </span><span class="n" id="mwmA">std</span><span class="p" id="mwmQ">.</span><span class="n" id="mwmg">stdio</span><span class="p" id="mwmw">;</span> <span class="kt" id="mwnA">void</span><span class="w" id="mwnQ"> </span><span class="n" id="mwng">main</span><span class="p" id="mwnw">()</span><span class="w" id="mwoA"> </span><span class="p" id="mwoQ">{</span> <span class="w" id="mwog"> </span><span class="kt" id="mwow">int</span><span class="w" id="mwpA"> </span><span class="n" id="mwpQ">multiplier</span><span class="w" id="mwpg"> </span><span class="p" id="mwpw">=</span><span class="w" id="mwqA"> </span><span class="mi" id="mwqQ">10</span><span class="p" id="mwqg">;</span> <span class="w" id="mwqw"> </span><span class="kt" id="mwrA">int</span><span class="w" id="mwrQ"> </span><span class="n" id="mwrg">scaled</span><span class="p" id="mwrw">(</span><span class="kt" id="mwsA">int</span><span class="w" id="mwsQ"> </span><span class="n" id="mwsg">x</span><span class="p" id="mwsw">)</span><span class="w" id="mwtA"> </span><span class="p" id="mwtQ">{</span> <span class="w" id="mwtg"> </span><span class="k" id="mwtw">return</span><span class="w" id="mwuA"> </span><span class="n" id="mwuQ">x</span><span class="w" id="mwug"> </span><span class="p" id="mwuw">*</span><span class="w" id="mwvA"> </span><span class="n" id="mwvQ">multiplier</span><span class="p" id="mwvg">;</span> <span class="w" id="mwvw"> </span><span class="p" id="mwwA">}</span> <span class="w" id="mwwQ"> </span><span class="k" id="mwwg">foreach</span><span class="w" id="mwww"> </span><span class="p" id="mwxA">(</span><span class="n" id="mwxQ">i</span><span class="p" id="mwxg">;</span><span class="w" id="mwxw"> </span><span class="mi" id="mwyA">0</span><span class="w" id="mwyQ"> </span><span class="p" id="mwyg">..</span><span class="w" id="mwyw"> </span><span class="mi" id="mwzA">10</span><span class="p" id="mwzQ">)</span><span class="w" id="mwzg"> </span><span class="p" id="mwzw">{</span> <span class="w" id="mw0A"> </span><span class="n" id="mw0Q">writefln</span><span class="p" id="mw0g">(</span><span class="s" id="mw0w">"Hello, world %d! scaled = %d"</span><span class="p" id="mw1A">,</span><span class="w" id="mw1Q"> </span><span class="n" id="mw1g">i</span><span class="p" id="mw1w">,</span><span class="w" id="mw2A"> </span><span class="n" id="mw2Q">scaled</span><span class="p" id="mw2g">(</span><span class="n" id="mw2w">i</span><span class="p" id="mw3A">));</span> <span class="w" id="mw3Q"> </span><span class="p" id="mw3g">}</span> <span class="p" id="mw3w">}</span>

Object-oriented

Object-oriented programming in D is based on a single inheritance hierarchy, with all classes derived from class Object. D does not support multiple inheritance; instead, it uses Java-style interfaces, which are comparable to C++'s pure abstract classes, and mixins, which separate common functionality from the inheritance hierarchy. D also allows the defining of static and final (non-virtual) methods in interfaces.

Interfaces and inheritance in D support covariant types for return types of overridden methods.

D supports type forwarding and optional custom dynamic dispatch.

Classes (and interfaces) in D can contain invariants which are automatically checked before and after entry to public methods, in accord with the design by contract methodology.

Many aspects of classes (and structs) can be introspected automatically at compile time (a form of reflective programming (reflection) using type traits) and at runtime (RTTI / TypeInfo), to facilitate generic code or automatic code generation (usually using compile-time techniques).

Functional

D supports functional programming features such as function literals, closures, recursively-immutable objects and the use of higher-order functions. There are two syntaxes for anonymous functions, including a multiple-statement form and a "shorthand" single-expression notation:

<span id="mw_w"></span><span class="kt" id="mwAQA">int</span><span class="w" id="mwAQE"> </span><span class="k" id="mwAQI">function</span><span class="p" id="mwAQM">(</span><span class="kt" id="mwAQQ">int</span><span class="p" id="mwAQU">)</span><span class="w" id="mwAQY"> </span><span class="n" id="mwAQc">g</span><span class="p" id="mwAQg">;</span> <span class="n" id="mwAQk">g</span><span class="w" id="mwAQo"> </span><span class="p" id="mwAQs">=</span><span class="w" id="mwAQw"> </span><span class="p" id="mwAQ0">(</span><span class="n" id="mwAQ4">x</span><span class="p" id="mwAQ8">)</span><span class="w" id="mwARA"> </span><span class="p" id="mwARE">{</span><span class="w" id="mwARI"> </span><span class="k" id="mwARM">return</span><span class="w" id="mwARQ"> </span><span class="n" id="mwARU">x</span><span class="w" id="mwARY"> </span><span class="p" id="mwARc">*</span><span class="w" id="mwARg"> </span><span class="n" id="mwARk">x</span><span class="p" id="mwARo">;</span><span class="w" id="mwARs"> </span><span class="p" id="mwARw">};</span><span class="w" id="mwAR0"> </span><span class="c1" id="mwAR4">// longhand</span> <span class="n" id="mwAR8">g</span><span class="w" id="mwASA"> </span><span class="p" id="mwASE">=</span><span class="w" id="mwASI"> </span><span class="p" id="mwASM">(</span><span class="n" id="mwASQ">x</span><span class="p" id="mwASU">)</span><span class="w" id="mwASY"> </span><span class="p" id="mwASc">=></span><span class="w" id="mwASg"> </span><span class="n" id="mwASk">x</span><span class="w" id="mwASo"> </span><span class="p" id="mwASs">*</span><span class="w" id="mwASw"> </span><span class="n" id="mwAS0">x</span><span class="p" id="mwAS4">;</span><span class="w" id="mwAS8"> </span><span class="c1" id="mwATA">// shorthand</span>

There are two built-in types for function literals, function, which is simply a pointer to a stack-allocated function, and delegate, which also includes a pointer to the relevant stack frame, the surrounding ‘environment’, which contains the current local variables. Type inference may be used with an anonymous function, in which case the compiler creates a delegate unless it can prove that an environment pointer is not necessary. Likewise, to implement a closure, the compiler places enclosed local variables on the heap only if necessary (for example, if a closure is returned by another function, and exits that function's scope). When using type inference, the compiler will also add attributes such as pure and nothrow to a function's type, if it can prove that they apply.

Other functional features such as currying and common higher-order functions such as map, filter, and reduce are available through the standard library modules std.functional and std.algorithm.

<span id="mwAUI"></span><span class="k" id="mwAUM">import</span><span class="w" id="mwAUQ"> </span><span class="n" id="mwAUU">std</span><span class="p" id="mwAUY">.</span><span class="n" id="mwAUc">stdio</span><span class="p" id="mwAUg">,</span><span class="w" id="mwAUk"> </span><span class="n" id="mwAUo">std</span><span class="p" id="mwAUs">.</span><span class="n" id="mwAUw">algorithm</span><span class="p" id="mwAU0">,</span><span class="w" id="mwAU4"> </span><span class="n" id="mwAU8">std</span><span class="p" id="mwAVA">.</span><span class="n" id="mwAVE">range</span><span class="p" id="mwAVI">;</span> <span class="kt" id="mwAVM">void</span><span class="w" id="mwAVQ"> </span><span class="n" id="mwAVU">main</span><span class="p" id="mwAVY">()</span><span class="w" id="mwAVc"> </span><span class="p" id="mwAVg">{</span> <span class="w" id="mwAVk"> </span><span class="kt" id="mwAVo">int</span><span class="p" id="mwAVs">[]</span><span class="w" id="mwAVw"> </span><span class="n" id="mwAV0">a1</span><span class="w" id="mwAV4"> </span><span class="p" id="mwAV8">=</span><span class="w" id="mwAWA"> </span><span class="p" id="mwAWE">[</span><span class="mi" id="mwAWI">0</span><span class="p" id="mwAWM">,</span><span class="w" id="mwAWQ"> </span><span class="mi" id="mwAWU">1</span><span class="p" id="mwAWY">,</span><span class="w" id="mwAWc"> </span><span class="mi" id="mwAWg">2</span><span class="p" id="mwAWk">,</span><span class="w" id="mwAWo"> </span><span class="mi" id="mwAWs">3</span><span class="p" id="mwAWw">,</span><span class="w" id="mwAW0"> </span><span class="mi" id="mwAW4">4</span><span class="p" id="mwAW8">,</span><span class="w" id="mwAXA"> </span><span class="mi" id="mwAXE">5</span><span class="p" id="mwAXI">,</span><span class="w" id="mwAXM"> </span><span class="mi" id="mwAXQ">6</span><span class="p" id="mwAXU">,</span><span class="w" id="mwAXY"> </span><span class="mi" id="mwAXc">7</span><span class="p" id="mwAXg">,</span><span class="w" id="mwAXk"> </span><span class="mi" id="mwAXo">8</span><span class="p" id="mwAXs">,</span><span class="w" id="mwAXw"> </span><span class="mi" id="mwAX0">9</span><span class="p" id="mwAX4">];</span> <span class="w" id="mwAX8"> </span><span class="kt" id="mwAYA">int</span><span class="p" id="mwAYE">[]</span><span class="w" id="mwAYI"> </span><span class="n" id="mwAYM">a2</span><span class="w" id="mwAYQ"> </span><span class="p" id="mwAYU">=</span><span class="w" id="mwAYY"> </span><span class="p" id="mwAYc">[</span><span class="mi" id="mwAYg">6</span><span class="p" id="mwAYk">,</span><span class="w" id="mwAYo"> </span><span class="mi" id="mwAYs">7</span><span class="p" id="mwAYw">,</span><span class="w" id="mwAY0"> </span><span class="mi" id="mwAY4">8</span><span class="p" id="mwAY8">,</span><span class="w" id="mwAZA"> </span><span class="mi" id="mwAZE">9</span><span class="p" id="mwAZI">];</span> <span class="w" id="mwAZM"> </span><span class="c1" id="mwAZQ">// must be immutable to allow access from inside a pure function</span> <span class="w" id="mwAZU"> </span><span class="k" id="mwAZY">immutable</span><span class="w" id="mwAZc"> </span><span class="n" id="mwAZg">pivot</span><span class="w" id="mwAZk"> </span><span class="p" id="mwAZo">=</span><span class="w" id="mwAZs"> </span><span class="mi" id="mwAZw">5</span><span class="p" id="mwAZ0">;</span> <span class="w" id="mwAZ4"> </span><span class="kt" id="mwAZ8">int</span><span class="w" id="mwAaA"> </span><span class="n" id="mwAaE">mySum</span><span class="p" id="mwAaI">(</span><span class="kt" id="mwAaM">int</span><span class="w" id="mwAaQ"> </span><span class="n" id="mwAaU">a</span><span class="p" id="mwAaY">,</span><span class="w" id="mwAac"> </span><span class="kt" id="mwAag">int</span><span class="w" id="mwAak"> </span><span class="n" id="mwAao">b</span><span class="p" id="mwAas">)</span><span class="w" id="mwAaw"> </span><span class="k" id="mwAa0">pure</span><span class="w" id="mwAa4"> </span><span class="k" id="mwAa8">nothrow</span><span class="w" id="mwAbA"> </span><span class="cm" id="mwAbE">/* pure function */</span><span class="w" id="mwAbI"> </span><span class="p" id="mwAbM">{</span> <span class="w" id="mwAbQ"> </span><span class="c1" id="mwAbU">// ref to enclosing-scope</span> <span class="w" id="mwAbY"> </span><span class="k" id="mwAbc">if</span><span class="w" id="mwAbg"> </span><span class="p" id="mwAbk">(</span><span class="n" id="mwAbo">b</span><span class="w" id="mwAbs"> </span><span class="p" id="mwAbw"><=</span><span class="w" id="mwAb0"> </span><span class="n" id="mwAb4">pivot</span><span class="p" id="mwAb8">)</span><span class="w" id="mwAcA"> </span><span class="p" id="mwAcE">{</span> <span class="w" id="mwAcI"> </span><span class="k" id="mwAcM">return</span><span class="w" id="mwAcQ"> </span><span class="n" id="mwAcU">a</span><span class="w" id="mwAcY"> </span><span class="p" id="mwAcc">+</span><span class="w" id="mwAcg"> </span><span class="n" id="mwAck">b</span><span class="p" id="mwAco">;</span> <span class="w" id="mwAcs"> </span><span class="p" id="mwAcw">}</span><span class="w" id="mwAc0"> </span><span class="k" id="mwAc4">else</span><span class="w" id="mwAc8"> </span><span class="p" id="mwAdA">{</span> <span class="w" id="mwAdE"> </span><span class="k" id="mwAdI">return</span><span class="w" id="mwAdM"> </span><span class="n" id="mwAdQ">a</span><span class="p" id="mwAdU">;</span> <span class="w" id="mwAdY"> </span><span class="p" id="mwAdc">}</span> <span class="w" id="mwAdg"> </span><span class="p" id="mwAdk">}</span> <span class="w" id="mwAdo"> </span><span class="c1" id="mwAds">// passing a delegate (closure)</span> <span class="w" id="mwAdw"> </span><span class="k" id="mwAd0">auto</span><span class="w" id="mwAd4"> </span><span class="n" id="mwAd8">result</span><span class="w" id="mwAeA"> </span><span class="p" id="mwAeE">=</span><span class="w" id="mwAeI"> </span><span class="n" id="mwAeM">reduce</span><span class="p" id="mwAeQ">!</span><span class="n" id="mwAeU">mySum</span><span class="p" id="mwAeY">(</span><span class="n" id="mwAec">chain</span><span class="p" id="mwAeg">(</span><span class="n" id="mwAek">a1</span><span class="p" id="mwAeo">,</span><span class="w" id="mwAes"> </span><span class="n" id="mwAew">a2</span><span class="p" id="mwAe0">));</span> <span class="w" id="mwAe4"> </span><span class="n" id="mwAe8">writeln</span><span class="p" id="mwAfA">(</span><span class="s" id="mwAfE">"Result: "</span><span class="p" id="mwAfI">,</span><span class="w" id="mwAfM"> </span><span class="n" id="mwAfQ">result</span><span class="p" id="mwAfU">);</span><span class="w" id="mwAfY"> </span><span class="c1" id="mwAfc">// Result: 15</span> <span class="w" id="mwAfg"> </span><span class="c1" id="mwAfk">// passing a delegate literal</span> <span class="w" id="mwAfo"> </span><span class="n" id="mwAfs">result</span><span class="w" id="mwAfw"> </span><span class="p" id="mwAf0">=</span><span class="w" id="mwAf4"> </span><span class="n" id="mwAf8">reduce</span><span class="p" id="mwAgA">!((</span><span class="n" id="mwAgE">a</span><span class="p" id="mwAgI">,</span><span class="w" id="mwAgM"> </span><span class="n" id="mwAgQ">b</span><span class="p" id="mwAgU">)</span><span class="w" id="mwAgY"> </span><span class="p" id="mwAgc">=></span><span class="w" id="mwAgg"> </span><span class="p" id="mwAgk">(</span><span class="n" id="mwAgo">b</span><span class="w" id="mwAgs"> </span><span class="p" id="mwAgw"><=</span><span class="w" id="mwAg0"> </span><span class="n" id="mwAg4">pivot</span><span class="p" id="mwAg8">)</span><span class="w" id="mwAhA"> </span><span class="p" id="mwAhE">?</span><span class="w" id="mwAhI"> </span><span class="n" id="mwAhM">a</span><span class="w" id="mwAhQ"> </span><span class="p" id="mwAhU">+</span><span class="w" id="mwAhY"> </span><span class="n" id="mwAhc">b</span><span class="w" id="mwAhg"> </span><span class="p" id="mwAhk">:</span><span class="w" id="mwAho"> </span><span class="n" id="mwAhs">a</span><span class="p" id="mwAhw">)(</span><span class="n" id="mwAh0">chain</span><span class="p" id="mwAh4">(</span><span class="n" id="mwAh8">a1</span><span class="p" id="mwAiA">,</span><span class="w" id="mwAiE"> </span><span class="n" id="mwAiI">a2</span><span class="p" id="mwAiM">));</span> <span class="w" id="mwAiQ"> </span><span class="n" id="mwAiU">writeln</span><span class="p" id="mwAiY">(</span><span class="s" id="mwAic">"Result: "</span><span class="p" id="mwAig">,</span><span class="w" id="mwAik"> </span><span class="n" id="mwAio">result</span><span class="p" id="mwAis">);</span><span class="w" id="mwAiw"> </span><span class="c1" id="mwAi0">// Result: 15</span> <span class="p" id="mwAi4">}</span>

Alternatively, the above function compositions can be expressed using Uniform function call syntax (UFCS) for more natural left-to-right reading:

<span id="mwAjM"></span><span class="k" id="mwAjQ">auto</span><span class="w" id="mwAjU"> </span><span class="n" id="mwAjY">result</span><span class="w" id="mwAjc"> </span><span class="p" id="mwAjg">=</span><span class="w" id="mwAjk"> </span><span class="n" id="mwAjo">a1</span><span class="p" id="mwAjs">.</span><span class="n" id="mwAjw">chain</span><span class="p" id="mwAj0">(</span><span class="n" id="mwAj4">a2</span><span class="p" id="mwAj8">).</span><span class="n" id="mwAkA">reduce</span><span class="p" id="mwAkE">!</span><span class="n" id="mwAkI">mySum</span><span class="p" id="mwAkM">();</span> <span class="n" id="mwAkQ">writeln</span><span class="p" id="mwAkU">(</span><span class="s" id="mwAkY">"Result: "</span><span class="p" id="mwAkc">,</span><span class="w" id="mwAkg"> </span><span class="n" id="mwAkk">result</span><span class="p" id="mwAko">);</span> <span class="n" id="mwAks">result</span><span class="w" id="mwAkw"> </span><span class="p" id="mwAk0">=</span><span class="w" id="mwAk4"> </span><span class="n" id="mwAk8">a1</span><span class="p" id="mwAlA">.</span><span class="n" id="mwAlE">chain</span><span class="p" id="mwAlI">(</span><span class="n" id="mwAlM">a2</span><span class="p" id="mwAlQ">).</span><span class="n" id="mwAlU">reduce</span><span class="p" id="mwAlY">!((</span><span class="n" id="mwAlc">a</span><span class="p" id="mwAlg">,</span><span class="w" id="mwAlk"> </span><span class="n" id="mwAlo">b</span><span class="p" id="mwAls">)</span><span class="w" id="mwAlw"> </span><span class="p" id="mwAl0">=></span><span class="w" id="mwAl4"> </span><span class="p" id="mwAl8">(</span><span class="n" id="mwAmA">b</span><span class="w" id="mwAmE"> </span><span class="p" id="mwAmI"><=</span><span class="w" id="mwAmM"> </span><span class="n" id="mwAmQ">pivot</span><span class="p" id="mwAmU">)</span><span class="w" id="mwAmY"> </span><span class="p" id="mwAmc">?</span><span class="w" id="mwAmg"> </span><span class="n" id="mwAmk">a</span><span class="w" id="mwAmo"> </span><span class="p" id="mwAms">+</span><span class="w" id="mwAmw"> </span><span class="n" id="mwAm0">b</span><span class="w" id="mwAm4"> </span><span class="p" id="mwAm8">:</span><span class="w" id="mwAnA"> </span><span class="n" id="mwAnE">a</span><span class="p" id="mwAnI">)();</span> <span class="n" id="mwAnM">writeln</span><span class="p" id="mwAnQ">(</span><span class="s" id="mwAnU">"Result: "</span><span class="p" id="mwAnY">,</span><span class="w" id="mwAnc"> </span><span class="n" id="mwAng">result</span><span class="p" id="mwAnk">);</span>

Parallelism

Parallel programming concepts are implemented in the library, and do not require extra support from the compiler. However the D type system and compiler ensure that data sharing can be detected and managed transparently.

<span id="mwAn4"></span><span class="k" id="mwAn8">import</span><span class="w" id="mwAoA"> </span><span class="n" id="mwAoE">std</span><span class="p" id="mwAoI">.</span><span class="n" id="mwAoM">stdio</span><span class="w" id="mwAoQ"> </span><span class="p" id="mwAoU">:</span><span class="w" id="mwAoY"> </span><span class="n" id="mwAoc">writeln</span><span class="p" id="mwAog">;</span> <span class="k" id="mwAok">import</span><span class="w" id="mwAoo"> </span><span class="n" id="mwAos">std</span><span class="p" id="mwAow">.</span><span class="n" id="mwAo0">range</span><span class="w" id="mwAo4"> </span><span class="p" id="mwAo8">:</span><span class="w" id="mwApA"> </span><span class="n" id="mwApE">iota</span><span class="p" id="mwApI">;</span> <span class="k" id="mwApM">import</span><span class="w" id="mwApQ"> </span><span class="n" id="mwApU">std</span><span class="p" id="mwApY">.</span><span class="n" id="mwApc">parallelism</span><span class="w" id="mwApg"> </span><span class="p" id="mwApk">:</span><span class="w" id="mwApo"> </span><span class="n" id="mwAps">parallel</span><span class="p" id="mwApw">;</span> <span class="kt" id="mwAp0">void</span><span class="w" id="mwAp4"> </span><span class="n" id="mwAp8">main</span><span class="p" id="mwAqA">()</span><span class="w" id="mwAqE"> </span><span class="p" id="mwAqI">{</span> <span class="w" id="mwAqM"> </span><span class="k" id="mwAqQ">foreach</span><span class="w" id="mwAqU"> </span><span class="p" id="mwAqY">(</span><span class="n" id="mwAqc">i</span><span class="p" id="mwAqg">;</span><span class="w" id="mwAqk"> </span><span class="n" id="mwAqo">iota</span><span class="p" id="mwAqs">(</span><span class="mi" id="mwAqw">11</span><span class="p" id="mwAq0">).</span><span class="n" id="mwAq4">parallel</span><span class="p" id="mwAq8">)</span><span class="w" id="mwArA"> </span><span class="p" id="mwArE">{</span> <span class="w" id="mwArI"> </span><span class="c1" id="mwArM">// The body of the foreach loop is executed in parallel for each i</span> <span class="w" id="mwArQ"> </span><span class="n" id="mwArU">writeln</span><span class="p" id="mwArY">(</span><span class="s" id="mwArc">"processing "</span><span class="p" id="mwArg">,</span><span class="w" id="mwArk"> </span><span class="n" id="mwAro">i</span><span class="p" id="mwArs">);</span> <span class="w" id="mwArw"> </span><span class="p" id="mwAr0">}</span> <span class="p" id="mwAr4">}</span>

iota(11).parallel is equivalent to std.parallelism.parallel(iota(11)) by using UFCS.

The same module also supports taskPool which can be used for dynamic creation of parallel tasks, and for map-filter-reduce and fold style operations on ranges (and arrays), which is useful when combined with functional operations. std.algorithm.map returns a lazily evaluated range rather than an array. This way, the elements are computed by each worker task in parallel automatically.

<span id="mwAsc"></span><span class="k" id="mwAsg">import</span><span class="w" id="mwAsk"> </span><span class="n" id="mwAso">std</span><span class="p" id="mwAss">.</span><span class="n" id="mwAsw">stdio</span><span class="w" id="mwAs0"> </span><span class="p" id="mwAs4">:</span><span class="w" id="mwAs8"> </span><span class="n" id="mwAtA">writeln</span><span class="p" id="mwAtE">;</span> <span class="k" id="mwAtI">import</span><span class="w" id="mwAtM"> </span><span class="n" id="mwAtQ">std</span><span class="p" id="mwAtU">.</span><span class="n" id="mwAtY">algorithm</span><span class="w" id="mwAtc"> </span><span class="p" id="mwAtg">:</span><span class="w" id="mwAtk"> </span><span class="n" id="mwAto">map</span><span class="p" id="mwAts">;</span> <span class="k" id="mwAtw">import</span><span class="w" id="mwAt0"> </span><span class="n" id="mwAt4">std</span><span class="p" id="mwAt8">.</span><span class="n" id="mwAuA">range</span><span class="w" id="mwAuE"> </span><span class="p" id="mwAuI">:</span><span class="w" id="mwAuM"> </span><span class="n" id="mwAuQ">iota</span><span class="p" id="mwAuU">;</span> <span class="k" id="mwAuY">import</span><span class="w" id="mwAuc"> </span><span class="n" id="mwAug">std</span><span class="p" id="mwAuk">.</span><span class="n" id="mwAuo">parallelism</span><span class="w" id="mwAus"> </span><span class="p" id="mwAuw">:</span><span class="w" id="mwAu0"> </span><span class="n" id="mwAu4">taskPool</span><span class="p" id="mwAu8">;</span> <span class="cm" id="mwAvA">/* On Intel i7-3930X and gdc 9.3.0:</span> <span class="cm" id="mwAvE"> * 5140ms using std.algorithm.reduce</span> <span class="cm" id="mwAvI"> * 888ms using std.parallelism.taskPool.reduce</span> <span class="cm" id="mwAvM"> *</span> <span class="cm" id="mwAvQ"> * On AMD Threadripper 2950X, and gdc 9.3.0:</span> <span class="cm" id="mwAvU"> * 2864ms using std.algorithm.reduce</span> <span class="cm" id="mwAvY"> * 95ms using std.parallelism.taskPool.reduce</span> <span class="cm" id="mwAvc"> */</span> <span class="kt" id="mwAvg">void</span><span class="w" id="mwAvk"> </span><span class="n" id="mwAvo">main</span><span class="p" id="mwAvs">()</span><span class="w" id="mwAvw"> </span><span class="p" id="mwAv0">{</span> <span class="w" id="mwAv4"> </span><span class="k" id="mwAv8">auto</span><span class="w" id="mwAwA"> </span><span class="n" id="mwAwE">nums</span><span class="w" id="mwAwI"> </span><span class="p" id="mwAwM">=</span><span class="w" id="mwAwQ"> </span><span class="n" id="mwAwU">iota</span><span class="p" id="mwAwY">(</span><span class="mf" id="mwAwc">1.0</span><span class="p" id="mwAwg">,</span><span class="w" id="mwAwk"> </span><span class="mf" id="mwAwo">1_000_000_000.0</span><span class="p" id="mwAws">);</span> <span class="w" id="mwAww"> </span><span class="k" id="mwAw0">auto</span><span class="w" id="mwAw4"> </span><span class="n" id="mwAw8">x</span><span class="w" id="mwAxA"> </span><span class="p" id="mwAxE">=</span><span class="w" id="mwAxI"> </span><span class="n" id="mwAxM">taskPool</span><span class="p" id="mwAxQ">.</span><span class="n" id="mwAxU">reduce</span><span class="p" id="mwAxY">!</span><span class="s" id="mwAxc">"a + b"</span><span class="p" id="mwAxg">(</span> <span class="w" id="mwAxk"> </span><span class="mf" id="mwAxo">0.0</span><span class="p" id="mwAxs">,</span><span class="w" id="mwAxw"> </span><span class="n" id="mwAx0">map</span><span class="p" id="mwAx4">!</span><span class="s" id="mwAx8">"1.0 / (a * a)"</span><span class="p" id="mwAyA">(</span><span class="n" id="mwAyE">nums</span><span class="p" id="mwAyI">)</span> <span class="w" id="mwAyM"> </span><span class="p" id="mwAyQ">);</span> <span class="w" id="mwAyU"> </span><span class="n" id="mwAyY">writeln</span><span class="p" id="mwAyc">(</span><span class="s" id="mwAyg">"Sum: "</span><span class="p" id="mwAyk">,</span><span class="w" id="mwAyo"> </span><span class="n" id="mwAys">x</span><span class="p" id="mwAyw">);</span> <span class="p" id="mwAy0">}</span>

Concurrency

Concurrency is fully implemented in the library, and it does not require support from the compiler. Alternative implementations and methodologies of writing concurrent code are possible. The use of D typing system does help ensure memory safety.

<span id="mwAzI"></span><span class="k" id="mwAzM">import</span><span class="w" id="mwAzQ"> </span><span class="n" id="mwAzU">std</span><span class="p" id="mwAzY">.</span><span class="n" id="mwAzc">stdio</span><span class="p" id="mwAzg">,</span><span class="w" id="mwAzk"> </span><span class="n" id="mwAzo">std</span><span class="p" id="mwAzs">.</span><span class="n" id="mwAzw">concurrency</span><span class="p" id="mwAz0">,</span><span class="w" id="mwAz4"> </span><span class="n" id="mwAz8">std</span><span class="p" id="mwA0A">.</span><span class="n" id="mwA0E">variant</span><span class="p" id="mwA0I">;</span> <span class="kt" id="mwA0M">void</span><span class="w" id="mwA0Q"> </span><span class="n" id="mwA0U">foo</span><span class="p" id="mwA0Y">()</span><span class="w" id="mwA0c"> </span><span class="p" id="mwA0g">{</span> <span class="w" id="mwA0k"> </span><span class="kt" id="mwA0o">bool</span><span class="w" id="mwA0s"> </span><span class="n" id="mwA0w">cont</span><span class="w" id="mwA00"> </span><span class="p" id="mwA04">=</span><span class="w" id="mwA08"> </span><span class="kc" id="mwA1A">true</span><span class="p" id="mwA1E">;</span> <span class="w" id="mwA1I"> </span><span class="k" id="mwA1M">while</span><span class="w" id="mwA1Q"> </span><span class="p" id="mwA1U">(</span><span class="n" id="mwA1Y">cont</span><span class="p" id="mwA1c">)</span><span class="w" id="mwA1g"> </span><span class="p" id="mwA1k">{</span> <span class="w" id="mwA1o"> </span><span class="c1" id="mwA1s">// Delegates are used to match the message type.</span> <span class="w" id="mwA1w"> </span><span class="n" id="mwA10">receive</span><span class="p" id="mwA14">(</span> <span class="w" id="mwA18"> </span><span class="p" id="mwA2A">(</span><span class="kt" id="mwA2E">int</span><span class="w" id="mwA2I"> </span><span class="n" id="mwA2M">msg</span><span class="p" id="mwA2Q">)</span><span class="w" id="mwA2U"> </span><span class="p" id="mwA2Y">=></span><span class="w" id="mwA2c"> </span><span class="n" id="mwA2g">writeln</span><span class="p" id="mwA2k">(</span><span class="s" id="mwA2o">"int received: "</span><span class="p" id="mwA2s">,</span><span class="w" id="mwA2w"> </span><span class="n" id="mwA20">msg</span><span class="p" id="mwA24">),</span> <span class="w" id="mwA28"> </span><span class="p" id="mwA3A">(</span><span class="n" id="mwA3E">Tid</span><span class="w" id="mwA3I"> </span><span class="n" id="mwA3M">sender</span><span class="p" id="mwA3Q">)</span><span class="w" id="mwA3U"> </span><span class="p" id="mwA3Y">{</span><span class="w" id="mwA3c"> </span><span class="n" id="mwA3g">cont</span><span class="w" id="mwA3k"> </span><span class="p" id="mwA3o">=</span><span class="w" id="mwA3s"> </span><span class="kc" id="mwA3w">false</span><span class="p" id="mwA30">;</span><span class="w" id="mwA34"> </span><span class="n" id="mwA38">sender</span><span class="p" id="mwA4A">.</span><span class="n" id="mwA4E">send</span><span class="p" id="mwA4I">(-</span><span class="mi" id="mwA4M">1</span><span class="p" id="mwA4Q">);</span><span class="w" id="mwA4U"> </span><span class="p" id="mwA4Y">},</span> <span class="w" id="mwA4c"> </span><span class="p" id="mwA4g">(</span><span class="n" id="mwA4k">Variant</span><span class="w" id="mwA4o"> </span><span class="n" id="mwA4s">v</span><span class="p" id="mwA4w">)</span><span class="w" id="mwA40"> </span><span class="p" id="mwA44">=></span><span class="w" id="mwA48"> </span><span class="n" id="mwA5A">writeln</span><span class="p" id="mwA5E">(</span><span class="s" id="mwA5I">"huh?"</span><span class="p" id="mwA5M">)</span><span class="w" id="mwA5Q"> </span><span class="c1" id="mwA5U">// Variant matches any type</span> <span class="w" id="mwA5Y"> </span><span class="p" id="mwA5c">);</span> <span class="w" id="mwA5g"> </span><span class="p" id="mwA5k">}</span> <span class="p" id="mwA5o">}</span> <span class="kt" id="mwA5s">void</span><span class="w" id="mwA5w"> </span><span class="n" id="mwA50">main</span><span class="p" id="mwA54">()</span><span class="w" id="mwA58"> </span><span class="p" id="mwA6A">{</span> <span class="w" id="mwA6E"> </span><span class="k" id="mwA6I">auto</span><span class="w" id="mwA6M"> </span><span class="n" id="mwA6Q">tid</span><span class="w" id="mwA6U"> </span><span class="p" id="mwA6Y">=</span><span class="w" id="mwA6c"> </span><span class="n" id="mwA6g">spawn</span><span class="p" id="mwA6k">(&</span><span class="n" id="mwA6o">foo</span><span class="p" id="mwA6s">);</span><span class="w" id="mwA6w"> </span><span class="c1" id="mwA60">// spawn a new thread running foo()</span> <span class="w" id="mwA64"> </span><span class="k" id="mwA68">foreach</span><span class="w" id="mwA7A"> </span><span class="p" id="mwA7E">(</span><span class="n" id="mwA7I">i</span><span class="p" id="mwA7M">;</span><span class="w" id="mwA7Q"> </span><span class="mi" id="mwA7U">0</span><span class="w" id="mwA7Y"> </span><span class="p" id="mwA7c">..</span><span class="w" id="mwA7g"> </span><span class="mi" id="mwA7k">10</span><span class="p" id="mwA7o">)</span><span class="w" id="mwA7s"> </span><span class="p" id="mwA7w">{</span> <span class="w" id="mwA70"> </span><span class="n" id="mwA74">tid</span><span class="p" id="mwA78">.</span><span class="n" id="mwA8A">send</span><span class="p" id="mwA8E">(</span><span class="n" id="mwA8I">i</span><span class="p" id="mwA8M">);</span><span class="w" id="mwA8Q"> </span><span class="c1" id="mwA8U">// send some integers</span> <span class="w" id="mwA8Y"> </span><span class="p" id="mwA8c">}</span> <span class="w" id="mwA8g"> </span><span class="n" id="mwA8k">tid</span><span class="p" id="mwA8o">.</span><span class="n" id="mwA8s">send</span><span class="p" id="mwA8w">(</span><span class="mf" id="mwA80">1.0f</span><span class="p" id="mwA84">);</span><span class="w" id="mwA88"> </span><span class="c1" id="mwA9A">// send a float</span> <span class="w" id="mwA9E"> </span><span class="n" id="mwA9I">tid</span><span class="p" id="mwA9M">.</span><span class="n" id="mwA9Q">send</span><span class="p" id="mwA9U">(</span><span class="s" id="mwA9Y">"hello"</span><span class="p" id="mwA9c">);</span><span class="w" id="mwA9g"> </span><span class="c1" id="mwA9k">// send a string</span> <span class="w" id="mwA9o"> </span><span class="n" id="mwA9s">tid</span><span class="p" id="mwA9w">.</span><span class="n" id="mwA90">send</span><span class="p" id="mwA94">(</span><span class="n" id="mwA98">thisTid</span><span class="p" id="mwA-A">);</span><span class="w" id="mwA-E"> </span><span class="c1" id="mwA-I">// send a struct (Tid)</span> <span class="w" id="mwA-M"> </span><span class="n" id="mwA-Q">receive</span><span class="p" id="mwA-U">((</span><span class="kt" id="mwA-Y">int</span><span class="w" id="mwA-c"> </span><span class="n" id="mwA-g">x</span><span class="p" id="mwA-k">)</span><span class="w" id="mwA-o"> </span><span class="p" id="mwA-s">=></span><span class="w" id="mwA-w"> </span><span class="n" id="mwA-0">writeln</span><span class="p" id="mwA-4">(</span><span class="s" id="mwA-8">"Main thread received message: "</span><span class="p" id="mwA_A">,</span><span class="w" id="mwA_E"> </span><span class="n" id="mwA_I">x</span><span class="p" id="mwA_M">));</span> <span class="p" id="mwA_Q">}</span>

Metaprogramming

Metaprogramming is supported through templates, compile-time function execution, tuples, and string mixins. The following examples demonstrate some of D's compile-time features.

Templates in D can be written in a more imperative style compared to the C++ functional style for templates. This is a regular function that calculates the factorial of a number:

<span id="mwA_0"></span><span class="kt" id="mwA_4">ulong</span><span class="w" id="mwA_8"> </span><span class="n" id="mwBAA">factorial</span><span class="p" id="mwBAE">(</span><span class="kt" id="mwBAI">ulong</span><span class="w" id="mwBAM"> </span><span class="n" id="mwBAQ">n</span><span class="p" id="mwBAU">)</span><span class="w" id="mwBAY"> </span><span class="p" id="mwBAc">{</span> <span class="w" id="mwBAg"> </span><span class="k" id="mwBAk">if</span><span class="w" id="mwBAo"> </span><span class="p" id="mwBAs">(</span><span class="n" id="mwBAw">n</span><span class="w" id="mwBA0"> </span><span class="p" id="mwBA4"><</span><span class="w" id="mwBA8"> </span><span class="mi" id="mwBBA">2</span><span class="p" id="mwBBE">)</span><span class="w" id="mwBBI"> </span><span class="p" id="mwBBM">{</span> <span class="w" id="mwBBQ"> </span><span class="k" id="mwBBU">return</span><span class="w" id="mwBBY"> </span><span class="mi" id="mwBBc">1</span><span class="p" id="mwBBg">;</span> <span class="w" id="mwBBk"> </span><span class="p" id="mwBBo">}</span><span class="w" id="mwBBs"> </span><span class="k" id="mwBBw">else</span><span class="w" id="mwBB0"> </span><span class="p" id="mwBB4">{</span> <span class="w" id="mwBB8"> </span><span class="k" id="mwBCA">return</span><span class="w" id="mwBCE"> </span><span class="n" id="mwBCI">n</span><span class="w" id="mwBCM"> </span><span class="p" id="mwBCQ">*</span><span class="w" id="mwBCU"> </span><span class="n" id="mwBCY">factorial</span><span class="p" id="mwBCc">(</span><span class="n" id="mwBCg">n</span><span class="p" id="mwBCk">-</span><span class="mi" id="mwBCo">1</span><span class="p" id="mwBCs">);</span> <span class="w" id="mwBCw"> </span><span class="p" id="mwBC0">}</span> <span class="p" id="mwBC4">}</span>

Here, the use of static if, D's compile-time conditional construct, is demonstrated to construct a template that performs the same calculation using code that is similar to that of the function above:

<span id="mwBDM"></span><span class="k" id="mwBDQ">template</span><span class="w" id="mwBDU"> </span><span class="n" id="mwBDY">Factorial</span><span class="p" id="mwBDc">(</span><span class="kt" id="mwBDg">ulong</span><span class="w" id="mwBDk"> </span><span class="n" id="mwBDo">n</span><span class="p" id="mwBDs">)</span><span class="w" id="mwBDw"> </span><span class="p" id="mwBD0">{</span> <span class="w" id="mwBD4"> </span><span class="k" id="mwBD8">static</span><span class="w" id="mwBEA"> </span><span class="k" id="mwBEE">if</span><span class="w" id="mwBEI"> </span><span class="p" id="mwBEM">(</span><span class="n" id="mwBEQ">n</span><span class="w" id="mwBEU"> </span><span class="p" id="mwBEY"><</span><span class="w" id="mwBEc"> </span><span class="mi" id="mwBEg">2</span><span class="p" id="mwBEk">)</span><span class="w" id="mwBEo"> </span><span class="p" id="mwBEs">{</span> <span class="w" id="mwBEw"> </span><span class="k" id="mwBE0">enum</span><span class="w" id="mwBE4"> </span><span class="n" id="mwBE8">Factorial</span><span class="w" id="mwBFA"> </span><span class="p" id="mwBFE">=</span><span class="w" id="mwBFI"> </span><span class="mi" id="mwBFM">1</span><span class="p" id="mwBFQ">;</span> <span class="w" id="mwBFU"> </span><span class="p" id="mwBFY">}</span><span class="w" id="mwBFc"> </span><span class="k" id="mwBFg">else</span><span class="w" id="mwBFk"> </span><span class="p" id="mwBFo">{</span> <span class="w" id="mwBFs"> </span><span class="k" id="mwBFw">enum</span><span class="w" id="mwBF0"> </span><span class="n" id="mwBF4">Factorial</span><span class="w" id="mwBF8"> </span><span class="p" id="mwBGA">=</span><span class="w" id="mwBGE"> </span><span class="n" id="mwBGI">n</span><span class="w" id="mwBGM"> </span><span class="p" id="mwBGQ">*</span><span class="w" id="mwBGU"> </span><span class="n" id="mwBGY">Factorial</span><span class="p" id="mwBGc">!(</span><span class="n" id="mwBGg">n</span><span class="p" id="mwBGk">-</span><span class="mi" id="mwBGo">1</span><span class="p" id="mwBGs">);</span> <span class="w" id="mwBGw"> </span><span class="p" id="mwBG0">}</span> <span class="p" id="mwBG4">}</span>

In the following two examples, the template and function defined above are used to compute factorials. The types of constants need not be specified explicitly as the compiler infers their types from the right-hand sides of assignments:

<span id="mwBHM"></span><span class="k" id="mwBHQ">enum</span><span class="w" id="mwBHU"> </span><span class="n" id="mwBHY">factorial7</span><span class="w" id="mwBHc"> </span><span class="p" id="mwBHg">=</span><span class="w" id="mwBHk"> </span><span class="n" id="mwBHo">Factorial</span><span class="p" id="mwBHs">!(</span><span class="mi" id="mwBHw">7</span><span class="p" id="mwBH0">);</span>

This is an example of compile-time function execution (CTFE). Ordinary functions may be used in constant, compile-time expressions provided they meet certain criteria:

<span id="mwBII"></span><span class="k" id="mwBIM">enum</span><span class="w" id="mwBIQ"> </span><span class="n" id="mwBIU">factorial9</span><span class="w" id="mwBIY"> </span><span class="p" id="mwBIc">=</span><span class="w" id="mwBIg"> </span><span class="n" id="mwBIk">factorial</span><span class="p" id="mwBIo">(</span><span class="mi" id="mwBIs">9</span><span class="p" id="mwBIw">);</span>

The std.string.format function performs printf-like data formatting (also at compile-time, through CTFE), and the "msg" pragma displays the result at compile time:

<span id="mwBJQ"></span><span class="k" id="mwBJU">import</span><span class="w" id="mwBJY"> </span><span class="n" id="mwBJc">std</span><span class="p" id="mwBJg">.</span><span class="nb" id="mwBJk">string</span><span class="w" id="mwBJo"> </span><span class="p" id="mwBJs">:</span><span class="w" id="mwBJw"> </span><span class="n" id="mwBJ0">format</span><span class="p" id="mwBJ4">;</span> <span class="k" id="mwBJ8">pragma</span><span class="p" id="mwBKA">(</span><span class="n" id="mwBKE">msg</span><span class="p" id="mwBKI">,</span><span class="w" id="mwBKM"> </span><span class="n" id="mwBKQ">format</span><span class="p" id="mwBKU">(</span><span class="s" id="mwBKY">"7! = %s"</span><span class="p" id="mwBKc">,</span><span class="w" id="mwBKg"> </span><span class="n" id="mwBKk">fact_7</span><span class="p" id="mwBKo">));</span> <span class="k" id="mwBKs">pragma</span><span class="p" id="mwBKw">(</span><span class="n" id="mwBK0">msg</span><span class="p" id="mwBK4">,</span><span class="w" id="mwBK8"> </span><span class="n" id="mwBLA">format</span><span class="p" id="mwBLE">(</span><span class="s" id="mwBLI">"9! = %s"</span><span class="p" id="mwBLM">,</span><span class="w" id="mwBLQ"> </span><span class="n" id="mwBLU">fact_9</span><span class="p" id="mwBLY">));</span>

String mixins, combined with compile-time function execution, allow for the generation of D code using string operations at compile time. This can be used to parse domain-specific languages, which will be compiled as part of the program:

<span id="mwBLs"></span><span class="c1" id="mwBLw">// hypothetical module which contains a function that parses Foo source code</span> <span class="c1" id="mwBL0">// and returns equivalent D code</span> <span class="k" id="mwBL4">import</span><span class="w" id="mwBL8"> </span><span class="n" id="mwBMA">FooToD</span><span class="p" id="mwBME">;</span> <span class="kt" id="mwBMI">void</span><span class="w" id="mwBMM"> </span><span class="n" id="mwBMQ">main</span><span class="p" id="mwBMU">()</span><span class="w" id="mwBMY"> </span><span class="p" id="mwBMc">{</span> <span class="w" id="mwBMg"> </span><span class="k" id="mwBMk">mixin</span><span class="p" id="mwBMo">(</span><span class="n" id="mwBMs">fooToD</span><span class="p" id="mwBMw">(</span><span class="k" id="mwBM0">import</span><span class="p" id="mwBM4">(</span><span class="s" id="mwBM8">"example.foo"</span><span class="p" id="mwBNA">)));</span> <span class="p" id="mwBNE">}</span>

Memory management

Memory is usually managed with garbage collection, but specific objects may be finalized immediately when they go out of scope. This is what the majority of programs and libraries written in D use.

Explicit memory management is possible using the overloaded operator new, by calling C's malloc and free directly, or implementing custom allocator schemes such as stack allocation with fallback, RAII-style allocation, reference counting, or shared reference counting. Garbage collection can be controlled: programmers may add and exclude memory ranges from being observed by the collector, can disable and enable the collector and force either a generational or full collection cycle. The language documentation provides examples of how to implement alternative memory management schemes for scenarios where garbage collection is not preferred.

In functions, struct instances are by default allocated on the stack, while class instances by default allocated on the heap (with only reference to the class instance being on the stack). However this can be changed for classes, for example using standard library template std.typecons.scoped, or by using new for structs and assigning to a pointer instead of a value-based variable.

In functions, static arrays (of known size) are allocated on the stack. For dynamic arrays, one can use the core.stdc.stdlib.alloca function (similar to alloca in C), to allocate memory on the stack. The returned pointer can be used (recast) into a (typed) dynamic array, by means of a slice (however resizing array, including appending must be avoided; and for obvious reasons they must not be returned from the function).

A scope keyword can be used both to annotate parts of code, but also variables and classes/structs, to indicate they should be destroyed (destructor called) immediately on scope exit. Whatever the memory is deallocated also depends on implementation and class-vs-struct differences.

std.experimental.allocator contains modular and composable allocator templates to create custom allocators for specific use cases.

SafeD

SafeD is the name given to the subset of D that can be guaranteed to be memory safe. Functions marked @safe are checked at compile time to ensure that they do not use any features that could result in corruption of memory, such as pointer arithmetic and unchecked casts. Any other functions called must also be marked as @safe or @trusted. Functions can be marked @trusted for the cases where the compiler cannot distinguish between safe use of a feature that is disabled in SafeD and a potential case of memory corruption.

Scope lifetime safety

Initially under the banners of DIP1000 and DIP25 (now part of the language specification), D provides protections against certain ill-formed constructions involving the lifetimes of data.

The current mechanisms in place primarily deal with function parameters and stack memory; however, the language design roadmap includes plans to expand lifetime tracking within the D programming language, drawing on concepts from the Rust programming language. (influenced by ideas from Rust programming language).

Lifetime safety of assignments

Within @safe code, the lifetime of an assignment involving a reference type is checked to ensure that the lifetime of the assignee is longer than that of the assigned.

For example:

<span id="mwBSc"></span><span class="nd" id="mwBSg">@safe</span><span class="w" id="mwBSk"> </span><span class="kt" id="mwBSo">void</span><span class="w" id="mwBSs"> </span><span class="n" id="mwBSw">test</span><span class="p" id="mwBS0">()</span><span class="w" id="mwBS4"> </span><span class="p" id="mwBS8">{</span> <span class="w" id="mwBTA"> </span><span class="kt" id="mwBTE">int</span><span class="w" id="mwBTI"> </span><span class="n" id="mwBTM">tmp</span><span class="w" id="mwBTQ"> </span><span class="p" id="mwBTU">=</span><span class="w" id="mwBTY"> </span><span class="mi" id="mwBTc">0</span><span class="p" id="mwBTg">;</span><span class="w" id="mwBTk"> </span><span class="c1" id="mwBTo">// #1</span> <span class="w" id="mwBTs"> </span><span class="kt" id="mwBTw">int</span><span class="p" id="mwBT0">*</span><span class="w" id="mwBT4"> </span><span class="n" id="mwBT8">rad</span><span class="p" id="mwBUA">;</span><span class="w" id="mwBUE"> </span><span class="c1" id="mwBUI">// #2</span> <span class="w" id="mwBUM"> </span><span class="n" id="mwBUQ">rad</span><span class="w" id="mwBUU"> </span><span class="p" id="mwBUY">=</span><span class="w" id="mwBUc"> </span><span class="p" id="mwBUg">&</span><span class="n" id="mwBUk">tmp</span><span class="p" id="mwBUo">;</span><span class="w" id="mwBUs"> </span><span class="c1" id="mwBUw">// If the order of the declarations of #1 and #2 is reversed, this fails.</span> <span class="w" id="mwBU0"> </span><span class="p" id="mwBU4">{</span> <span class="w" id="mwBU8"> </span><span class="kt" id="mwBVA">int</span><span class="w" id="mwBVE"> </span><span class="n" id="mwBVI">bad</span><span class="w" id="mwBVM"> </span><span class="p" id="mwBVQ">=</span><span class="w" id="mwBVU"> </span><span class="mi" id="mwBVY">45</span><span class="p" id="mwBVc">;</span><span class="w" id="mwBVg"> </span><span class="c1" id="mwBVk">// The lifetime of "bad" only extends to the scope in which it is defined.</span> <span class="w" id="mwBVo"> </span><span class="p" id="mwBVs">*</span><span class="n" id="mwBVw">rad</span><span class="w" id="mwBV0"> </span><span class="p" id="mwBV4">=</span><span class="w" id="mwBV8"> </span><span class="n" id="mwBWA">bad</span><span class="p" id="mwBWE">;</span><span class="w" id="mwBWI"> </span><span class="c1" id="mwBWM">// This is valid.</span> <span class="w" id="mwBWQ"> </span><span class="n" id="mwBWU">rad</span><span class="w" id="mwBWY"> </span><span class="p" id="mwBWc">=</span><span class="w" id="mwBWg"> </span><span class="p" id="mwBWk">&</span><span class="n" id="mwBWo">bad</span><span class="p" id="mwBWs">;</span><span class="w" id="mwBWw"> </span><span class="c1" id="mwBW0">// The lifetime of rad is longer than bad, hence this is not valid.</span> <span class="w" id="mwBW4"> </span><span class="p" id="mwBW8">}</span> <span class="p" id="mwBXA">}</span>

Function parameter lifetime annotations within @safe code

When applied to function parameter which are either of pointer type or references, the keywords return and scope constrain the lifetime and use of that parameter.

The language standard dictates the following behaviour:

An annotated example is given below.

<span id="mwBYw"></span><span class="nd" id="mwBY0">@safe</span><span class="p" id="mwBY4">:</span> <span class="kt" id="mwBY8">int</span><span class="p" id="mwBZA">*</span><span class="w" id="mwBZE"> </span><span class="n" id="mwBZI">gp</span><span class="p" id="mwBZM">;</span> <span class="kt" id="mwBZQ">void</span><span class="w" id="mwBZU"> </span><span class="n" id="mwBZY">thorin</span><span class="p" id="mwBZc">(</span><span class="k" id="mwBZg">scope</span><span class="w" id="mwBZk"> </span><span class="kt" id="mwBZo">int</span><span class="p" id="mwBZs">*);</span> <span class="kt" id="mwBZw">void</span><span class="w" id="mwBZ0"> </span><span class="n" id="mwBZ4">gloin</span><span class="p" id="mwBZ8">(</span><span class="kt" id="mwBaA">int</span><span class="p" id="mwBaE">*);</span> <span class="kt" id="mwBaI">int</span><span class="p" id="mwBaM">*</span><span class="w" id="mwBaQ"> </span><span class="n" id="mwBaU">balin</span><span class="p" id="mwBaY">(</span><span class="k" id="mwBac">return</span><span class="w" id="mwBag"> </span><span class="k" id="mwBak">scope</span><span class="w" id="mwBao"> </span><span class="kt" id="mwBas">int</span><span class="p" id="mwBaw">*</span><span class="w" id="mwBa0"> </span><span class="n" id="mwBa4">p</span><span class="p" id="mwBa8">,</span><span class="w" id="mwBbA"> </span><span class="k" id="mwBbE">scope</span><span class="w" id="mwBbI"> </span><span class="kt" id="mwBbM">int</span><span class="p" id="mwBbQ">*</span><span class="w" id="mwBbU"> </span><span class="n" id="mwBbY">q</span><span class="p" id="mwBbc">,</span><span class="w" id="mwBbg"> </span><span class="kt" id="mwBbk">int</span><span class="p" id="mwBbo">*</span><span class="w" id="mwBbs"> </span><span class="n" id="mwBbw">r</span><span class="p" id="mwBb0">)</span><span class="w" id="mwBb4"> </span><span class="p" id="mwBb8">{</span> <span class="w" id="mwBcA"> </span><span class="n" id="mwBcE">gp</span><span class="w" id="mwBcI"> </span><span class="p" id="mwBcM">=</span><span class="w" id="mwBcQ"> </span><span class="n" id="mwBcU">p</span><span class="p" id="mwBcY">;</span><span class="w" id="mwBcc"> </span><span class="c1" id="mwBcg">// Error, p escapes to global variable gp.</span> <span class="w" id="mwBck"> </span><span class="n" id="mwBco">gp</span><span class="w" id="mwBcs"> </span><span class="p" id="mwBcw">=</span><span class="w" id="mwBc0"> </span><span class="n" id="mwBc4">q</span><span class="p" id="mwBc8">;</span><span class="w" id="mwBdA"> </span><span class="c1" id="mwBdE">// Error, q escapes to global variable gp.</span> <span class="w" id="mwBdI"> </span><span class="n" id="mwBdM">gp</span><span class="w" id="mwBdQ"> </span><span class="p" id="mwBdU">=</span><span class="w" id="mwBdY"> </span><span class="n" id="mwBdc">r</span><span class="p" id="mwBdg">;</span><span class="w" id="mwBdk"> </span><span class="c1" id="mwBdo">// OK.</span> <span class="w" id="mwBds"> </span><span class="n" id="mwBdw">thorin</span><span class="p" id="mwBd0">(</span><span class="n" id="mwBd4">p</span><span class="p" id="mwBd8">);</span><span class="w" id="mwBeA"> </span><span class="c1" id="mwBeE">// OK, p does not escape thorin().</span> <span class="w" id="mwBeI"> </span><span class="n" id="mwBeM">thorin</span><span class="p" id="mwBeQ">(</span><span class="n" id="mwBeU">q</span><span class="p" id="mwBeY">);</span><span class="w" id="mwBec"> </span><span class="c1" id="mwBeg">// OK.</span> <span class="w" id="mwBek"> </span><span class="n" id="mwBeo">thorin</span><span class="p" id="mwBes">(</span><span class="n" id="mwBew">r</span><span class="p" id="mwBe0">);</span><span class="w" id="mwBe4"> </span><span class="c1" id="mwBe8">// OK.</span> <span class="w" id="mwBfA"> </span><span class="n" id="mwBfE">gloin</span><span class="p" id="mwBfI">(</span><span class="n" id="mwBfM">p</span><span class="p" id="mwBfQ">);</span><span class="w" id="mwBfU"> </span><span class="c1" id="mwBfY">// Error, p escapes gloin().</span> <span class="w" id="mwBfc"> </span><span class="n" id="mwBfg">gloin</span><span class="p" id="mwBfk">(</span><span class="n" id="mwBfo">q</span><span class="p" id="mwBfs">);</span><span class="w" id="mwBfw"> </span><span class="c1" id="mwBf0">// Error, q escapes gloin().</span> <span class="w" id="mwBf4"> </span><span class="n" id="mwBf8">gloin</span><span class="p" id="mwBgA">(</span><span class="n" id="mwBgE">r</span><span class="p" id="mwBgI">);</span><span class="w" id="mwBgM"> </span><span class="c1" id="mwBgQ">// OK that r escapes gloin().</span> <span class="w" id="mwBgU"> </span><span class="k" id="mwBgY">return</span><span class="w" id="mwBgc"> </span><span class="n" id="mwBgg">p</span><span class="p" id="mwBgk">;</span><span class="w" id="mwBgo"> </span><span class="c1" id="mwBgs">// OK.</span> <span class="w" id="mwBgw"> </span><span class="k" id="mwBg0">return</span><span class="w" id="mwBg4"> </span><span class="n" id="mwBg8">q</span><span class="p" id="mwBhA">;</span><span class="w" id="mwBhE"> </span><span class="c1" id="mwBhI">// Error, cannot return 'scope' q.</span> <span class="w" id="mwBhM"> </span><span class="k" id="mwBhQ">return</span><span class="w" id="mwBhU"> </span><span class="n" id="mwBhY">r</span><span class="p" id="mwBhc">;</span><span class="w" id="mwBhg"> </span><span class="c1" id="mwBhk">// OK.</span> <span class="p" id="mwBho">}</span>

Interaction with other systems

C's application binary interface (ABI) is supported, as well as all of C's fundamental and derived types, enabling direct access to existing C code and libraries. D bindings are available for many popular C libraries. Additionally, C's standard library is part of standard D.

On Microsoft Windows, D can access Component Object Model (COM) code.

As long as memory management is properly performed, many other languages can be mixed with D in a single binary. For example, the GDC compiler allows to link and intermix C, C++, and other supported language codes such as Objective-C. D code (functions) can also be marked as using C, C++, Pascal ABIs, and thus be passed to the libraries written in these languages as callbacks. Similarly data can be interchanged between the codes written in these languages in both ways. This usually restricts use to primitive types, pointers, some forms of arrays, unions, structs, and only some types of function pointers.

Because many other programming languages often provide the C application programming interface (API) for writing extensions or running the interpreter of the languages, D can interface directly with these languages also, using standard C bindings (with a thin D interface file). For example, bi-directional bindings exist for the languages Python, Lua, and others, often using compile-time code generation and compile-time type reflection methods.

Interaction with C++ code

For D code marked as extern(C++), the following features are specified:

• The name mangling conventions shall match those of C++ on the target.
• For function calls, the ABI shall be equivalent.
• The vtable shall be matched up to single inheritance (the only level supported by the D language specification).

C++ namespaces are used via the syntax

<span id="mwBkQ"></span><span class="k" id="mwBkU">extern</span><span class="p" id="mwBkY">(</span><span class="n" id="mwBkc">C</span><span class="o" id="mwBkg">++</span><span class="p" id="mwBkk">,</span><span class="w" id="mwBko"> </span><span class="k" id="mwBks">namespace</span><span class="p" id="mwBkw">)</span>

where namespace is the name of the C++ namespace.

An example of C++ interoperation

On C++:

<span id="mwBlM"></span><span class="k" id="mwBlQ">import</span><span class="w" id="mwBlU"> </span><span class="n" id="mwBlY">std</span><span class="p" id="mwBlc">;</span> <span class="k" id="mwBlg">class</span><span class="w" id="mwBlk"> </span><span class="nc" id="mwBlo">Base</span><span class="w" id="mwBls"> </span><span class="p" id="mwBlw">{</span> <span class="k" id="mwBl0">public</span><span class="o" id="mwBl4">:</span> <span class="w" id="mwBl8"> </span><span class="k" id="mwBmA">virtual</span><span class="w" id="mwBmE"> </span><span class="kt" id="mwBmI">void</span><span class="w" id="mwBmM"> </span><span class="n" id="mwBmQ">print3i</span><span class="p" id="mwBmU">(</span><span class="kt" id="mwBmY">int</span><span class="w" id="mwBmc"> </span><span class="n" id="mwBmg">a</span><span class="p" id="mwBmk">,</span><span class="w" id="mwBmo"> </span><span class="kt" id="mwBms">int</span><span class="w" id="mwBmw"> </span><span class="n" id="mwBm0">b</span><span class="p" id="mwBm4">,</span><span class="w" id="mwBm8"> </span><span class="kt" id="mwBnA">int</span><span class="w" id="mwBnE"> </span><span class="n" id="mwBnI">c</span><span class="p" id="mwBnM">)</span><span class="w" id="mwBnQ"> </span><span class="o" id="mwBnU">=</span><span class="w" id="mwBnY"> </span><span class="mi" id="mwBnc">0</span><span class="p" id="mwBng">;</span> <span class="p" id="mwBnk">};</span> <span class="k" id="mwBno">class</span><span class="w" id="mwBns"> </span><span class="nc" id="mwBnw">Derived</span><span class="w" id="mwBn0"> </span><span class="o" id="mwBn4">:</span><span class="w" id="mwBn8"> </span><span class="k" id="mwBoA">public</span><span class="w" id="mwBoE"> </span><span class="n" id="mwBoI">Base</span><span class="w" id="mwBoM"> </span><span class="p" id="mwBoQ">{</span> <span class="k" id="mwBoU">private</span><span class="o" id="mwBoY">:</span> <span class="w" id="mwBoc"> </span><span class="kt" id="mwBog">int</span><span class="w" id="mwBok"> </span><span class="n" id="mwBoo">field</span><span class="p" id="mwBos">;</span> <span class="k" id="mwBow">public</span><span class="o" id="mwBo0">:</span> <span class="w" id="mwBo4"> </span><span class="k" id="mwBo8">explicit</span><span class="w" id="mwBpA"> </span><span class="n" id="mwBpE">Derived</span><span class="p" id="mwBpI">(</span><span class="kt" id="mwBpM">int</span><span class="w" id="mwBpQ"> </span><span class="n" id="mwBpU">field</span><span class="p" id="mwBpY">)</span><span class="o" id="mwBpc">:</span><span class="w" id="mwBpg"> </span> <span class="w" id="mwBpk"> </span><span class="n" id="mwBpo">field</span><span class="p" id="mwBps">(</span><span class="n" id="mwBpw">field</span><span class="p" id="mwBp0">)</span><span class="w" id="mwBp4"> </span><span class="p" id="mwBp8">{}</span> <span class="w" id="mwBqA"> </span><span class="kt" id="mwBqE">void</span><span class="w" id="mwBqI"> </span><span class="n" id="mwBqM">print3i</span><span class="p" id="mwBqQ">(</span><span class="kt" id="mwBqU">int</span><span class="w" id="mwBqY"> </span><span class="n" id="mwBqc">a</span><span class="p" id="mwBqg">,</span><span class="w" id="mwBqk"> </span><span class="kt" id="mwBqo">int</span><span class="w" id="mwBqs"> </span><span class="n" id="mwBqw">b</span><span class="p" id="mwBq0">,</span><span class="w" id="mwBq4"> </span><span class="kt" id="mwBq8">int</span><span class="w" id="mwBrA"> </span><span class="n" id="mwBrE">c</span><span class="p" id="mwBrI">)</span><span class="w" id="mwBrM"> </span><span class="p" id="mwBrQ">{</span> <span class="w" id="mwBrU"> </span><span class="n" id="mwBrY">std</span><span class="o" id="mwBrc">::</span><span class="n" id="mwBrg">println</span><span class="p" id="mwBrk">(</span><span class="s" id="mwBro">"a = {}"</span><span class="p" id="mwBrs">,</span><span class="w" id="mwBrw"> </span><span class="n" id="mwBr0">a</span><span class="p" id="mwBr4">);</span> <span class="w" id="mwBr8"> </span><span class="n" id="mwBsA">std</span><span class="o" id="mwBsE">::</span><span class="n" id="mwBsI">println</span><span class="p" id="mwBsM">(</span><span class="s" id="mwBsQ">"b = {}"</span><span class="p" id="mwBsU">,</span><span class="w" id="mwBsY"> </span><span class="n" id="mwBsc">b</span><span class="p" id="mwBsg">);</span> <span class="w" id="mwBsk"> </span><span class="n" id="mwBso">std</span><span class="o" id="mwBss">::</span><span class="n" id="mwBsw">println</span><span class="p" id="mwBs0">(</span><span class="s" id="mwBs4">"c = {}"</span><span class="p" id="mwBs8">,</span><span class="w" id="mwBtA"> </span><span class="n" id="mwBtE">c</span><span class="p" id="mwBtI">);</span> <span class="w" id="mwBtM"> </span><span class="p" id="mwBtQ">}</span> <span class="w" id="mwBtU"> </span><span class="kt" id="mwBtY">int</span><span class="w" id="mwBtc"> </span><span class="n" id="mwBtg">mul</span><span class="p" id="mwBtk">(</span><span class="kt" id="mwBto">int</span><span class="w" id="mwBts"> </span><span class="n" id="mwBtw">factor</span><span class="p" id="mwBt0">)</span><span class="w" id="mwBt4"> </span><span class="p" id="mwBt8">{</span> <span class="w" id="mwBuA"> </span><span class="k" id="mwBuE">return</span><span class="w" id="mwBuI"> </span><span class="n" id="mwBuM">field</span><span class="w" id="mwBuQ"> </span><span class="o" id="mwBuU">*</span><span class="w" id="mwBuY"> </span><span class="n" id="mwBuc">factor</span><span class="p" id="mwBug">;</span> <span class="w" id="mwBuk"> </span><span class="p" id="mwBuo">}</span> <span class="p" id="mwBus">};</span> <span class="n" id="mwBuw">Derived</span><span class="o" id="mwBu0">*</span><span class="w" id="mwBu4"> </span><span class="nf" id="mwBu8">createInstance</span><span class="p" id="mwBvA">(</span><span class="kt" id="mwBvE">int</span><span class="w" id="mwBvI"> </span><span class="n" id="mwBvM">i</span><span class="p" id="mwBvQ">)</span><span class="w" id="mwBvU"> </span><span class="p" id="mwBvY">{</span> <span class="w" id="mwBvc"> </span><span class="k" id="mwBvg">return</span><span class="w" id="mwBvk"> </span><span class="k" id="mwBvo">new</span><span class="w" id="mwBvs"> </span><span class="n" id="mwBvw">Derived</span><span class="p" id="mwBv0">(</span><span class="n" id="mwBv4">i</span><span class="p" id="mwBv8">);</span> <span class="p" id="mwBwA">}</span> <span class="kt" id="mwBwE">void</span><span class="w" id="mwBwI"> </span><span class="nf" id="mwBwM">deleteInstance</span><span class="p" id="mwBwQ">(</span><span class="n" id="mwBwU">Derived</span><span class="o" id="mwBwY">*&</span><span class="w" id="mwBwc"> </span><span class="n" id="mwBwg">d</span><span class="p" id="mwBwk">)</span><span class="w" id="mwBwo"> </span><span class="p" id="mwBws">{</span> <span class="w" id="mwBww"> </span><span class="k" id="mwBw0">delete</span><span class="w" id="mwBw4"> </span><span class="n" id="mwBw8">d</span><span class="p" id="mwBxA">;</span> <span class="w" id="mwBxE"> </span><span class="n" id="mwBxI">d</span><span class="w" id="mwBxM"> </span><span class="o" id="mwBxQ">=</span><span class="w" id="mwBxU"> </span><span class="mi" id="mwBxY">0</span><span class="p" id="mwBxc">;</span> <span class="p" id="mwBxg">}</span>

On D:

<span id="mwBxw"></span><span class="k" id="mwBx0">extern</span><span class="p" id="mwBx4">(</span><span class="n" id="mwBx8">C</span><span class="p" id="mwByA">++)</span><span class="w" id="mwByE"> </span><span class="p" id="mwByI">{</span> <span class="w" id="mwByM"> </span><span class="k" id="mwByQ">abstract</span><span class="w" id="mwByU"> </span><span class="k" id="mwByY">class</span><span class="w" id="mwByc"> </span><span class="n" id="mwByg">Base</span><span class="w" id="mwByk"> </span><span class="p" id="mwByo">{</span> <span class="w" id="mwBys"> </span><span class="k" id="mwByw">public</span><span class="p" id="mwBy0">:</span> <span class="w" id="mwBy4"> </span><span class="kt" id="mwBy8">void</span><span class="w" id="mwBzA"> </span><span class="n" id="mwBzE">print3i</span><span class="p" id="mwBzI">(</span><span class="kt" id="mwBzM">int</span><span class="w" id="mwBzQ"> </span><span class="n" id="mwBzU">a</span><span class="p" id="mwBzY">,</span><span class="w" id="mwBzc"> </span><span class="kt" id="mwBzg">int</span><span class="w" id="mwBzk"> </span><span class="n" id="mwBzo">b</span><span class="p" id="mwBzs">,</span><span class="w" id="mwBzw"> </span><span class="kt" id="mwBz0">int</span><span class="w" id="mwBz4"> </span><span class="n" id="mwBz8">c</span><span class="p" id="mwB0A">);</span> <span class="w" id="mwB0E"> </span><span class="p" id="mwB0I">}</span> <span class="w" id="mwB0M"> </span><span class="k" id="mwB0Q">class</span><span class="w" id="mwB0U"> </span><span class="n" id="mwB0Y">Derived</span><span class="w" id="mwB0c"> </span><span class="p" id="mwB0g">:</span><span class="w" id="mwB0k"> </span><span class="n" id="mwB0o">Base</span><span class="w" id="mwB0s"> </span><span class="p" id="mwB0w">{</span> <span class="w" id="mwB00"> </span><span class="k" id="mwB04">private</span><span class="p" id="mwB08">:</span> <span class="w" id="mwB1A"> </span><span class="kt" id="mwB1E">int</span><span class="w" id="mwB1I"> </span><span class="n" id="mwB1M">field</span><span class="p" id="mwB1Q">;</span> <span class="w" id="mwB1U"> </span><span class="k" id="mwB1Y">public</span><span class="p" id="mwB1c">:</span> <span class="w" id="mwB1g"> </span><span class="nd" id="mwB1k">@disable</span><span class="w" id="mwB1o"> </span><span class="k" id="mwB1s">this</span><span class="p" id="mwB1w">();</span> <span class="w" id="mwB10"> </span><span class="k" id="mwB14">override</span><span class="w" id="mwB18"> </span><span class="kt" id="mwB2A">void</span><span class="w" id="mwB2E"> </span><span class="n" id="mwB2I">print3i</span><span class="p" id="mwB2M">(</span><span class="kt" id="mwB2Q">int</span><span class="w" id="mwB2U"> </span><span class="n" id="mwB2Y">a</span><span class="p" id="mwB2c">,</span><span class="w" id="mwB2g"> </span><span class="kt" id="mwB2k">int</span><span class="w" id="mwB2o"> </span><span class="n" id="mwB2s">b</span><span class="p" id="mwB2w">,</span><span class="w" id="mwB20"> </span><span class="kt" id="mwB24">int</span><span class="w" id="mwB28"> </span><span class="n" id="mwB3A">c</span><span class="p" id="mwB3E">);</span> <span class="w" id="mwB3I"> </span><span class="k" id="mwB3M">final</span><span class="w" id="mwB3Q"> </span><span class="kt" id="mwB3U">int</span><span class="w" id="mwB3Y"> </span><span class="n" id="mwB3c">mul</span><span class="p" id="mwB3g">(</span><span class="kt" id="mwB3k">int</span><span class="w" id="mwB3o"> </span><span class="n" id="mwB3s">factor</span><span class="p" id="mwB3w">);</span> <span class="w" id="mwB30"> </span><span class="p" id="mwB34">}</span> <span class="w" id="mwB38"> </span><span class="n" id="mwB4A">Derived</span><span class="w" id="mwB4E"> </span><span class="n" id="mwB4I">createInstance</span><span class="p" id="mwB4M">(</span><span class="kt" id="mwB4Q">int</span><span class="w" id="mwB4U"> </span><span class="n" id="mwB4Y">i</span><span class="p" id="mwB4c">);</span> <span class="w" id="mwB4g"> </span><span class="kt" id="mwB4k">void</span><span class="w" id="mwB4o"> </span><span class="n" id="mwB4s">deleteInstance</span><span class="p" id="mwB4w">(</span><span class="k" id="mwB40">ref</span><span class="w" id="mwB44"> </span><span class="n" id="mwB48">Derived</span><span class="w" id="mwB5A"> </span><span class="n" id="mwB5E">d</span><span class="p" id="mwB5I">);</span> <span class="p" id="mwB5M">}</span> <span class="kt" id="mwB5Q">void</span><span class="w" id="mwB5U"> </span><span class="n" id="mwB5Y">main</span><span class="p" id="mwB5c">()</span><span class="w" id="mwB5g"> </span><span class="p" id="mwB5k">{</span> <span class="w" id="mwB5o"> </span><span class="k" id="mwB5s">import</span><span class="w" id="mwB5w"> </span><span class="n" id="mwB50">std</span><span class="p" id="mwB54">.</span><span class="n" id="mwB58">stdio</span><span class="p" id="mwB6A">;</span> <span class="w" id="mwB6E"> </span><span class="k" id="mwB6I">auto</span><span class="w" id="mwB6M"> </span><span class="n" id="mwB6Q">d1</span><span class="w" id="mwB6U"> </span><span class="p" id="mwB6Y">=</span><span class="w" id="mwB6c"> </span><span class="n" id="mwB6g">createInstance</span><span class="p" id="mwB6k">(</span><span class="mi" id="mwB6o">5</span><span class="p" id="mwB6s">);</span> <span class="w" id="mwB6w"> </span><span class="n" id="mwB60">writeln</span><span class="p" id="mwB64">(</span><span class="n" id="mwB68">d1</span><span class="p" id="mwB7A">.</span><span class="n" id="mwB7E">field</span><span class="p" id="mwB7I">);</span> <span class="w" id="mwB7M"> </span><span class="n" id="mwB7Q">writeln</span><span class="p" id="mwB7U">(</span><span class="n" id="mwB7Y">d1</span><span class="p" id="mwB7c">.</span><span class="n" id="mwB7g">mul</span><span class="p" id="mwB7k">(</span><span class="mi" id="mwB7o">4</span><span class="p" id="mwB7s">));</span> <span class="w" id="mwB7w"> </span><span class="n" id="mwB70">Base</span><span class="w" id="mwB74"> </span><span class="n" id="mwB78">b1</span><span class="w" id="mwB8A"> </span><span class="p" id="mwB8E">=</span><span class="w" id="mwB8I"> </span><span class="n" id="mwB8M">d1</span><span class="p" id="mwB8Q">;</span> <span class="w" id="mwB8U"> </span><span class="n" id="mwB8Y">b1</span><span class="p" id="mwB8c">.</span><span class="n" id="mwB8g">print3i</span><span class="p" id="mwB8k">(</span><span class="mi" id="mwB8o">1</span><span class="p" id="mwB8s">,</span><span class="w" id="mwB8w"> </span><span class="mi" id="mwB80">2</span><span class="p" id="mwB84">,</span><span class="w" id="mwB88"> </span><span class="mi" id="mwB9A">3</span><span class="p" id="mwB9E">);</span> <span class="w" id="mwB9I"> </span><span class="n" id="mwB9M">deleteInstance</span><span class="p" id="mwB9Q">(</span><span class="n" id="mwB9U">d1</span><span class="p" id="mwB9Y">);</span> <span class="w" id="mwB9c"> </span><span class="k" id="mwB9g">assert</span><span class="p" id="mwB9k">(</span><span class="n" id="mwB9o">d1</span><span class="w" id="mwB9s"> </span><span class="k" id="mwB9w">is</span><span class="w" id="mwB90"> </span><span class="kc" id="mwB94">null</span><span class="p" id="mwB98">);</span> <span class="w" id="mwB-A"> </span><span class="k" id="mwB-E">auto</span><span class="w" id="mwB-I"> </span><span class="n" id="mwB-M">d2</span><span class="w" id="mwB-Q"> </span><span class="p" id="mwB-U">=</span><span class="w" id="mwB-Y"> </span><span class="n" id="mwB-c">createInstance</span><span class="p" id="mwB-g">(</span><span class="mi" id="mwB-k">42</span><span class="p" id="mwB-o">);</span> <span class="w" id="mwB-s"> </span><span class="n" id="mwB-w">writeln</span><span class="p" id="mwB-0">(</span><span class="n" id="mwB-4">d2</span><span class="p" id="mwB-8">.</span><span class="n" id="mwB_A">field</span><span class="p" id="mwB_E">);</span> <span class="w" id="mwB_I"> </span><span class="n" id="mwB_M">deleteInstance</span><span class="p" id="mwB_Q">(</span><span class="n" id="mwB_U">d2</span><span class="p" id="mwB_Y">);</span> <span class="w" id="mwB_c"> </span><span class="k" id="mwB_g">assert</span><span class="p" id="mwB_k">(</span><span class="n" id="mwB_o">d2</span><span class="w" id="mwB_s"> </span><span class="k" id="mwB_w">is</span><span class="w" id="mwB_0"> </span><span class="kc" id="mwB_4">null</span><span class="p" id="mwB_8">);</span> <span class="p" id="mwCAA">}</span>

Better C

The D programming language has an official subset known as "Better C". This subset forbids access to D features requiring use of runtime libraries other than that of C.

Enabled via the compiler flags "-betterC" on DMD and LDC, and "-fno-druntime" on GDC, Better C may only call into D code compiled under the same flag (and linked code other than D) but code compiled without the Better C option may call into code compiled with it: this will, however, lead to slightly different behaviours due to differences in how C and D handle asserts.

Features included in Better C

• Unrestricted use of compile-time features (for example, D's dynamic allocation features can be used at compile time to pre-allocate D data)
• Full metaprogramming facilities
• Nested functions, nested structs, delegates and lambdas
• Member functions, constructors, destructors, operating overloading, etc.
• The full module system
• Array slicing, and array bounds checking
• RAII
• scope(exit)
• Memory safety protections
• Interfacing with C++
• COM classes and C++ classes
• assert failures are directed to the C runtime library
• switch with strings
• final switch
• unittest blocks
• printf() format validation

Features excluded from Better C

• Garbage collection
• TypeInfo and ModuleInfo
• Built-in threading (e.g. core.thread)
• Dynamic arrays (though slices of static arrays work) and associative arrays
• Exceptions
• synchronized and core.sync
• Static module constructors or destructors