Restriction on interface function types

[monarch_dodra]

On Wednesday, 12 March 2014 at 13:34:33 UTC, Steve Teale wrote:
> On Wednesday, 12 March 2014 at 13:12:20 UTC, Steven 
> Schveighoffer wrote:
>> On Wed, 12 Mar 2014 09:05:05 -0400, Steve Teale 
>> <steve.teale at britseyeview.com> wrote:
>
>> How is the compiler to build it's one copy of bad? Should x be 
>> typed as A or B? Or something not even seen in this module 
>> that could derive from I?
>>
>> -Steve
>
> Let's take bad() away, and instead:
>
> class A : I
> {
>    A myType() { return cast(A)null;}
>    final void foo();
> }
>
> class B : I
> {
>    B myType() {return cast(B) null;}
>    final void bar();
> }
>
> void main()
> {
>    I[] arr = [new A, new B];
>    foreach(i; arr) { (cast(typeof(i.myType()) i).foo() }
> }
>
> myType() is a virtual function, so calling it through the 
> interface type should get the correct version right?, and then 
> the cast should cause a call to A or B.

It will *call* the correct version, but the signature used will 
still statically be the interface's signature.

It can make a difference when you *statically* know you are in a 
derived type:

I i = new A();
A a = new A();

I ii = i.myType();
A aa = a.myType();

Here, the call to "myType", in both cases, will "runtime" resolve 
to A.myType().
*However*, the static type used to return the value, will not be 
the same.