Declaring interfaces with a constructor

[David Zhang via Digitalmars-d-learn]

What it says on the tin. Is there a way to create interfaces with 
a constructor or must I use an abstract class.

Additionally, is there a way to force the linker to link a 
function in a class without an implementation with another that 
does have an implementation?

i.e.

---
    //module a;
    class Foo {
        void fun();
    }

    import b: Foo;

    //module b;
    class Foo {
        void fun() { import std.stdio; writeln("!"); }
    }
---

Or something like this? Thanks.