How to 'add' functions to existing type/class/struct/interface...

[Adam D. Ruppe]

> How to 'add' functions to existing type/class/struct/interface...

You don't. It seems to be that this would break encapsulation anyway.

> I read from Adam that it is possible and is done within Phobos by D.
> Could some one provide some sample code to explain that.

Look in std.range for full examples but here's a brief one:

void doSomething(T)(T item) if( isMyInterface!T ) {
     // use item here
}

template isMyInterface(T) {
     static if(is(typeof(
           // write some code to test the interface here
     )))
         enum bool isMyInterface = true;
     else
         enum bool isMyInterface = false;
}



You can also use the template straight up, though that's less
structured:

auto doSomething(T)(T obj) {
     // write whatever you want here using obj
     // it won't compile if the obj doesn't match the used functions
}



Or, you can go with a more strictly Go style by using method #1
and automating the isMyInterface detection. Kenju Hara wrote
an adaptTo function that does something like this:

interface Interface {
    void foo();
}


class A { // note it doesn't list the interface here
     void foo();
}

void func(Interface i) { }


A a = new A();

func(adaptTo!Interface(a));


I don't think this has been committed to Phobos yet though.