concepts 0.0.4

Concepts for D

Right now there's only models, which can be used as a UDA or in a static assert:

    void checkFoo(T)()
    {
        T t = T.init;
        t.foo();
    }

    enum isFoo(T) = is(typeof(checkFoo!T));

    @models!(Foo, isFoo) //as a UDA
    struct Foo
    {
        void foo() {}
        static assert(models!(Foo, isFoo)); //as a static assert
    }

Here a template constraint isFoo is guaranteed to be true for type Foo. The difference between this and a regular static assert is that when the predicate fails the code for checkFoo is instantiated anyway so that the user knows why it failed to compile.