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#

D is a general-purpose programming language with static typing, systems-level access, and C-like syntax. With the D Programming Language, write fast, read fast, and run fast.
Fast code, fast.

Downloads Latest version: 2.103.1 – Changelog
your code here

Got a brief example illustrating D?

Submit your code to the digitalmars.D forum specifying "[your code here]" in the subject.

Upon approval it will be showcased here on a random schedule.

Compute average line length for stdin
`The D programming language Modern convenience. Modeling power. Native efficiency.`

    void main()
    {
        import std.range, std.stdio;

        auto sum = 0.0;
        auto count = stdin
            //Get an input range set up to read one line at a time
            .byLine
            //Perform a transparent operation (as in the shell command tee)
            .tee!(l => sum += l.length)
            .walkLength;

        writeln("Average line length: ",
            count ? sum / count : 0);
    }

Round floating point numbers
`2.4 plus 2.4 equals 5 for sufficiently large values of 2.`

    import std.algorithm, std.conv, std.functional,
        std.math, std.regex, std.stdio;

    alias round = pipe!(to!real, std.math.round, to!string);
    static reFloatingPoint = ctRegex!`[0-9]+\.[0-9]+`;

    void main()
    {
        // Replace anything that looks like a real
        // number with the rounded equivalent.
        stdin
            .byLine
            .map!(l => l.replaceAll!(c => c.hit.round)
                                    (reFloatingPoint))
            .each!writeln;
    }

Sort lines
`Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune`

    import std.stdio, std.array, std.algorithm;

    void main()
    {
        stdin
            .byLineCopy
            .array
            .sort!((a, b) => a > b) // descending order
            .each!writeln;
    }

Sort an Array at Compile-Time

    void main()
    {
        import std.algorithm, std.stdio;

        "Starting program".writeln;

        enum a = [ 3, 1, 2, 4, 0 ];
        // Sort data at compile-time
        static immutable b = sort(a);

        // Print the result _during_ compilation
        pragma(msg, "Finished compilation: ", b);
    }

Invoke external programs

    void main()
    {
        import std.exception, std.stdio, std.process;

        auto result = ["whoami"].execute;
        enforce(result.status == 0);
        result.output.write;
    }

Print hex dump

    void main()
    {
        import std.algorithm, std.stdio, std.file, std.range;
        enum cols = 14;
        // Split file into 14-byte chunks per row
        thisExePath.File("rb").byChunk(cols).take(20).each!(chunk =>
            // Use range formatting to format the
            // hexadecimal part and align the text part
            writefln!"%(%02X %)%*s  %s"(
                chunk,
                3 * (cols - chunk.length), "", // Padding
                chunk.map!(c => // Replace non-printable
                    c < 0x20 || c > 0x7E ? '.' : char(c))));
    }

Start a minimal web server

    #!/usr/bin/env dub
    /+ dub.sdl:
    dependency "vibe-d" version="~>0.9.0"
    +/
    void main()
    {
        import vibe.d;
        listenHTTP(":8080", (req, res) {
            res.writeBody("Hello, World: " ~ req.path);
        });
        runApplication();
    }

Initialize an Array in parallel

    void main()
    {
        import std.datetime.stopwatch : benchmark;
        import std.math, std.parallelism, std.stdio;

        auto logs = new double[100_000];
        auto bm = benchmark!({
            foreach (i, ref elem; logs)
                elem = log(1.0 + i);
        }, {
            foreach (i, ref elem; logs.parallel)
                elem = log(1.0 + i);
        })(100); // number of executions of each tested function
        writefln("Linear init: %s msecs", bm[0].total!"msecs");
        writefln("Parallel init: %s msecs", bm[1].total!"msecs");
    }

Sort in-place across multiple arrays

    void main()
    {
        import std.stdio : writefln;
        import std.algorithm.sorting : sort;
        import std.range : chain;

        int[] arr1 = [4, 9, 7];
        int[] arr2 = [5, 2, 1, 10];
        int[] arr3 = [6, 8, 3];
        // @nogc functions are guaranteed by the compiler
        // to be without any GC allocation
        () @nogc {
            sort(chain(arr1, arr2, arr3));
        }();
        writefln("%s\n%s\n%s\n", arr1, arr2, arr3);
    }

Count frequencies of character pairs

    void main()
    {
        import std.stdio : writefln;
        // An associative array mapping pairs of characters to integers
        int[char[2]] aa;
        auto arr = "ABBBA";

        // Iterate over all pairs in the string
        // ['A', 'B'], ['B', 'B'], ..., ['B', 'A']
        foreach (i; 0 .. arr.length - 1)
        {
            // String slicing doesn't allocate a copy
            char[2] pair = arr[i .. i + 2];
            // count occurrences
            aa[pair]++;
        }
        foreach (key, value; aa)
            writefln("key: %s, value: %d", key, value);
    }

Tiny RPN calculator
`2 3 3 4 + * *`

    void main()
    {
        import std.stdio, std.string, std.algorithm, std.conv;

        // Reduce the RPN expression using a stack
        readln.split.fold!((stack, op)
        {
            switch (op)
            {
                // Generate operator switch cases statically
                static foreach (c; "+-*/")
                    case [c]:
                        return stack[0 .. $ - 2] ~
                            mixin("stack[$ - 2] " ~ c ~
                                " stack[$ - 1]");
                default: return stack ~ op.to!real;
            }
        })((real[]).init).writeln;
    }

Subtyping with alias this

    struct Point
    {
        private double[2] p;
        // Forward all undefined symbols to p
        alias p this;
        double dot(Point rhs)
        {
            return p[0] * rhs.p[0] + p[1] * rhs.p[1];
        }
    }
    void main()
    {
        import std.stdio : writeln;
        // Point behaves like a `double[2]` ...
        Point p1, p2; p1 = [2, 1], p2 = [1, 1];
        assert(p1[$ - 1] == 1);
        // ... but with extended functionality
        writeln("p1 dot p2 = ", p1.dot(p2));
    }

## Support the D language

D is made possible through the hard work and dedication of many volunteers, with the coordination and outreach of the D Language Foundation, a 501(c)(3) non-profit organization. You can help further the development of the D language and help grow our community by supporting the Foundation.

Donate Learn More About The Foundation
Lots of to our sponsors and contributors.

### Industry Proven

Tweets by D_Programming

#### News

Stay updated with the latest posts in the Official D Blog from January 5, 2023: Memory Safety in a Systems Programming Language Part 3 by Ate Eskola.

From October 8, 2022: Memory Safety in a Modern Systems Programming Language Part 2 by Ate Eskola.

#### Learn

Take the Tour, explore major features in D, browse the quick overview, start with C or C++ background, and ask questions in the Learn forum.

For a deeper dive into D check out books or videos such as Ali Çehreli's free book Programming in D.

#### Community

Discuss D on the forums, join the IRC channel, read our official Blog, or follow us on Twitter. Browse the wiki, where among other things you can find the high-level vision of the D Language Foundation.

#### Documentation

Refer to the language specification and the documentation of Phobos, D's standard library. The DMD manual tells you how to use the compiler. Read various articles to deepen your understanding.

#### Contribute

Report any bugs you find to our bug tracker. If you can fix an issue, make a pull request on GitHub. There are many other ways to help, too!

#### Packages

DUB is the package manager for D. Get started with DUB, and check out the available packages.

#### Run

Configure linting, formatting or completion for your favorite IDE, editor or use run.dlang.io to play and experiment with D code.

#### Explore

Learn about pragmatic D, the DStyle, common D idioms and templates, See what's coming upcoming with next version, explore D Improvement Proposals, and don't fear D's garbage collection.

## Fast code, fast.

### Write Fast

D allows writing large code fragments without redundantly specifying types, like dynamic languages do. On the other hand, static inference deduces types and other code properties, giving the best of both the static and the dynamic worlds.

    void main()
    {
        // Define an array of numbers, double[].
        // Compiler recognizes the common
        // type of all initializers.
        auto arr = [ 1, 2, 3.14, 5.1, 6 ];
        // Dictionary that maps string to int,
        // type is spelled int[string]
        auto dictionary = [ "one" : 1, "two" : 2,
            "three" : 3 ];
        // Calls the min function defined below
        auto x = min(arr[0], dictionary["two"]);
    }
    // Type deduction works for function results.
    // This is important for generic functions,
    // such as min below, which works correctly
    // for all comparable types.
    auto min(T1, T2)(T1 lhs, T2 rhs)
    {
        return rhs < lhs ? rhs : lhs;
    }

Automatic memory management makes for safe, simple, and robust code. D also supports scoped resource management (aka the RAII idiom) and scope statements for deterministic transactional code that is easy to write and read.

    import std.stdio;

    class Widget { }

    void main()
    {
        // Automatically managed.
        auto w = new Widget;
        // Code is executed in any case upon scope exit.
        scope(exit) { writeln("Exiting main."); }
        // File is closed deterministically at scope's end.
        foreach (line; File(__FILE_FULL_PATH__).byLine())
        {
            writeln(line);
        }
        writeln();
    }

Built-in linear and associative arrays, slices, and ranges make daily programming simple and pleasant for tasks, both small and large.

`The D programming language Modern convenience. Modeling power. Native efficiency.`

    // Compute average line length for stdin
    void main()
    {
        import std.range, std.stdio;

        auto sum = 0.0;
        auto count = stdin.byLine
            .tee!(l => sum += l.length).walkLength;

        writeln("Average line length: ",
            count ? sum / count : 0);
    }

### Read Fast

The best paradigm is to not impose something at the expense of others. D offers classic polymorphism, value semantics, functional style, generics, generative programming, contract programming, and more—all harmoniously integrated.

    // Interfaces and classes
    interface Printable
    {
       void print(uint level)
       // contract is part of the interface
       in { assert(level > 0); }
    }

    // Interface implementation
    class Widget : Printable
    {
       void print(uint level)
       in{ }
       do{ }
    }

    // Single inheritance of state
    class ExtendedWidget : Widget
    {
       override void print(uint level)
       in { /* weakening precondition is okay */  }
       do
       {
           //... level may be 0 here ...
       }
    }

    // Immutable data shared across threads
    immutable string programName = "demo";
    // Mutable data is thread-local
    int perThread = 42;
    // Explicitly shared data
    shared int perApp = 5;

    // Structs have value semantics
    struct BigNum
    {
        // intercept copying
        this(this) { }
        // intercept destructor
        ~this() { }
    }

    void main()
    {
        // ...
    }

D offers an innovative approach to concurrency, featuring true immutable data, message passing, no sharing by default, and controlled mutable sharing across threads. Read more.

From simple scripts to large projects, D has the breadth to scale with any application's needs: unit testing, information hiding, refined modularity, fast compilation, precise interfaces. Read more.

### Run Fast

D compiles naturally to efficient native code.

D is designed such that most "obvious" code is fast and safe. On occasion a function might need to escape the confines of type safety for ultimate speed and control. For such rare cases D offers native pointers, type casts, access to any C function without any intervening translation, manual memory management, custom allocators and even inline assembly code.

    import core.stdc.stdlib;

    void livingDangerously()
    {
        // Access to C's malloc and free primitives
        enum bytes = float.sizeof * 1024 * 1024;
        auto buf = malloc(bytes);
        // free automatically upon scope exit
        scope(exit) free(buf);
        // Interprets memory as an array of floats
        auto floats = cast(float[]) buf[0 .. bytes];
        // Even stack allocation is possible
        auto moreBuf = alloca(4096 * 100);
        //...
    }

    // Using inline asm for extra speed on x86
    uint checked_multiply(uint x, uint y)
    {
        uint result;
        version (D_InlineAsm_X86)
        {
            // Inline assembler "sees" D variables and labels.
            asm
            {
                mov     EAX,x        ;
                mul     EAX,y        ;
                mov     result,EAX   ;
                jc      Loverflow    ;
            }
            return result;
        }
        else
        {
            result = x * y;
            if (!y || x <= uint.max / y)
               return result;
       }
    Loverflow:
       throw new Exception("multiply overflow");
    }

    void main()
    {
        // ...
    }

The @safe, @trusted, and @system function attributes allow the programmer to best decide the safety-efficiency tradeoffs of an application, and have the compiler check for consistency. Read more.

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