The D Programming Language

D has a totally redesigned and highly flexible template system. For starters, the ! operator is used for template instantiation. This eliminates the numerous ambiguities caused by <> instantiation and is more readily recognizable. Here is a simple copier template:

template TCopy(t) {
        void copy(T from, out T to)
        {
                to = from;
        }
}

void main()
{
        int from = 7;
        int to;
        TCopy!(int).copy(from, to);
}

Template declarations can be aliased:

alias TFoo!(int) temp;

Templates can be specialized for different types, and the compiler deduces which type you are referring to:

template TFoo(T)        { ... } // #1
template TFoo(T : T[])  { ... } // #2
template TFoo(T : char) { ... } // #3
template TFoo(T,U,V)    { ... } // #4
alias TFoo!(int) foo1;          // instantiates #1
alias TFoo!(double[]) foo2;     // instantiates #2
                                // with T being double
alias TFoo!(char) foo3;        // instantiates #3
alias TFoo!(char, int) fooe;   // error, number of
                               // arguments mismatch
alias TFoo!(char, int, int) foo4; // instantiates #4

If a template has one member function and nothing else, it can be declared like this:

void TFunk(T) (T i)
{
..
}

Function templates can be instantiated implicitly, and the types of the arguments deduced:

TFoo!(int, char[]) (2,"foo");
TFoo(2, "foo");

In those cases when you need to declare a template and its only member is a class, use the following simplified syntax:

class MyTemplateClass (T)
{
..
}

A mixin is just like cutting and pasting a template's code into a class; it doesn't create its own scope:

template TFoo(t)
{
        t i;
}

class test
{
        mixin TFoo!(int);
        this()
        {
                i = 5;
        }
}

void main()
{
        Test t = new Test;
        writefln(t.i);
}

D is a promising language that is able to supply many different needs in the programming community. Features such as arrays, SH syntax and type inference make D comparable to languages, such as Ruby and Python, in those regards, while still leaving the door open for low-level system programmers with the inline assembler and other features. D can be applied to many programming paradigms—be they object-oriented with classes and interfaces, generic programming with templates and mixins, procedural programming with functions and arrays, or any other. The garbage collector relieves the programmer of the need to manage all memory chunks manually, while still making it possible for those situations in which manual memory management is preferred. It brings in features of imperative languages, such as Lisp, with the lazy storage class, which drastically speeds up efficiency. The language is relatively stable, with the occasional new features or changes added in.

In short, D is a language ready for real-world deployment.