typeid() broken for interfaces?

[Maxim Fomin]

On Monday, 3 December 2012 at 23:53:26 UTC, deadalnix wrote:
> On Monday, 3 December 2012 at 21:53:47 UTC, Walter Bright wrote:
>> I really don't know what issue you're trying to solve here. 
>> The typeid's work fine - and interfaces are not objects. 
>> Having the typeid for an interface be an object means you 
>> cannot compare typeids of one interface to another interface.
>>
>
> You can't instantiate interface. So an underlying type MUST 
> exist. The whole point of typeid on expression is to discover 
> what is the dynamic type of things, otherwize you'd be using 
> typeid(type) not typeid(expression).

You cannot create interface instance with new operator because 
interface object is not valid until it is actually some class 
instance. But this does not mean neither that typeid operator for 
interfaces should return dynamic type nor that interface can be 
implicitly converted to Object - because interface instance may 
be invalid:

import std.stdio;

interface I { }

void main()
{
	I i;
         // should be implicitly converted
	Object o = cast(Object)i;
	writeln(typeid(o));
}

and because presence of interface does not necessarily mean that 
some class has implemented it.

This makes casting interfaces to object unsafe operation that 
better should require explicit cast.