http://code.dlang.org/packages/concepts

concepts is a dub package and library that allows one to declare that a struct conforms to a "compile-time interface" such as `isInputRange`. The difference between this and a simple `static assert(isInputRange!MyType)` is that when the static assert fails you have no idea why not and half of the time it's because of a typo (e.g. `popFrnt`). With concepts you get an error message from the compiler, and you can still use your concepts in template constraints.

It also has its own version of `isInputRange` et al that are drop-in replacements for the ones in Phobos, but you get compiler error messages instead of nothing.

The new addition is `@implements`:

interface IFoo {
    int foo(int i, string s) @safe;
    double lefoo(string s) @safe;
}

@implements!(Foo, IFoo)
struct Foo {
    int foo(int i, string s) @safe { return 0; }
    double lefoo(string s) @safe { return 0; }
}

// doesn't compile: Foo doesn't "implement" IFoo
/*
@implements!(Oops, IFoo)
struct Oops {}
*/

// also doesn't compile because foo is @system:
/*
@implements!(Nearly, IFoo)
struct Nearly {
    int foo(int i, string s) @system { return 0; }
    double lefoo(string s) @safe { return 0; }
}
*/

On Wednesday, 10 May 2017 at 10:53:59 UTC, Atila Neves wrote:
> concepts is a dub package and library that allows one to declare that a struct conforms to a "compile-time interface" such as `isInputRange`.

Awesome!

On Wednesday, 10 May 2017 at 10:53:59 UTC, Atila Neves wrote:
> http://code.dlang.org/packages/concepts
>
> concepts is a dub package and library that allows one to declare that a struct conforms to a "compile-time interface" such as `isInputRange`. The difference between this and a simple `static assert(isInputRange!MyType)` is that when the static assert fails you have no idea why not and half of the time it's because of a typo (e.g. `popFrnt`). With concepts you get an error message from the compiler, and you can still use your concepts in template constraints.

Niiiiice, I love constraints but there error messages aren't the best.