On Friday, 29 March 2019 at 23:44:35 UTC, Alex wrote:
> interface iBase
> {
> iBase fooBase(iBase);
> }
>
>
> class cBase : iBase
> {
> cBase fooBase(cBase c) { return c; }
>
> }
>
> cBase.fooBase should be a valid override of iBase.fooBase
> because
> they are the same type!
The return value there is allowed, but the parameter is not. Consider this case:
class AnotherChild : iBase { /* snip */ }
iBase i = new cBase(); // allowed, cBase implements iBase
i.fooBase(new AnotherChild);
That second line should be allowed: the interface says it accepts any
implementation of the iBase interface.
But the cBase implementation doen't allow *any* implementation of iBase - it
only accepts cBase and down. That function wouldn't be able to handle my
AnotherChild instance.
Thus, cBase.fooBase does NOT implement the iBase's interface, and it fails to
compile.
