According to https://dlang.org/spec/interface.html #10 this program should compile:

```ifa.d
interface D
{
    int foo();
}

class A : D
{
    int foo() { return 1; }
}

class B : A
{
    int foo() { return 2; }
}

void main ()
{
   import std.stdio;
   B b = new B();
   writeln (b.foo());  // returns 2
   D d = cast(D) b;    // ok since B inherits A's D implementation
   writeln (d.foo());  // returns 2;
}
```

$ dmd ifa
ifa.d(13): Error: cannot implicitly override base class method ifa.A.foo with ifa.B.foo; add override attribute

$ dmd --version
DMD64 D Compiler v2.082.0
Copyright (C) 1999-2018 by The D Language Foundation, All Rights Reserved written by Walter Bright