interface I
{
    bool opEquals(I i);
}

class C : I
{
    bool opEquals(I i)
    {
        return true;
    }
}

void main()
{
    I i1 = new C;
    I i2 = new C;
    assert(i1 == i2);  // Assertino failure
    assert(i1 != i2);  // Passes, although it's the opposite of what I want..
}

What's missing?

On Wednesday, 5 December 2012 at 00:17:05 UTC, deed wrote:
> interface I
> {
>     bool opEquals(I i);
> }
>
> class C : I
> {
>     bool opEquals(I i)
>     {
>         return true;
>     }
> }
>
> void main()
> {
>     I i1 = new C;
>     I i2 = new C;
>     assert(i1 == i2);  // Assertino failure
>     assert(i1 != i2);  // Passes, although it's the opposite of what I want..
> }
>
> What's missing?

It looks like you want the opEquals to be called and it is not. Match the signature of it to what is in object.di. This may be what you want.
----------------------------------

import std.stdio;
interface I
{
  bool opEquals(Object i);
}

class C : I
{
  override bool opEquals(Object i) const
  {
    writeln("Called");
    return true;
  }
}

void main()
{
  I i1 = new C;
  I i2 = new C;
  writeln(i1 == i2);
  writeln(i1 != i2);
}