[Issue 14612] typeid(interface) returns TypeInfo_Class object

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=14612

--- Comment #5 from Kenji Hara <k.hara.pg at gmail.com> ---
(In reply to Rainer Schuetze from comment #4)
> cast(Object) creates a call into the runtime (_d_interface_cast) and is
> pretty expensive. It could be optimized to the series of indirections by the
> compiler, though.

Actually _d_interface_cast is not so high cost so Object has no base class and
implements no interfaces.

> I guess the current behaviour could be described as "typeid(I) evaluates to
> the most derived interface that is implemented by the object and that
> inherits from the static type."
> 
> But "most derived" is not well defined when it comes to inheriting from
> multiple interfaces:

It would be visible when you consider the class object layout.

> interface I {}
> interface J : I {}
> interface K : I {}
> class E : J, K {}

//      I   I
// E :  J,  K
//===============

//      ij  ik
//      |   |
//      j   k
//      |   |
// e --[x]-[y]

[x] is the "most derived vptr slot of ij, and [y] is of ik.

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