• kdevel (30/30) Dec 24 2020 I would expect the unittest below to pass. Could not find
• Adam D. Ruppe (6/6) Dec 24 2020 Interfaces always give their own typeid, this is because they

kdevel <kdevel vogtner.de> writes:

I would expect the unittest below to pass. Could not find
any explanation in [1].

~~~typeid.d
class A {}
class B : A {}
class C : B {}

interface Q {}
class R : Q {}
class S : R {}

unittest {
    import std.stdio : writeln;

    void runtest (X, Y) ()
    {
       X x = new Y ();
       writeln ("X = ", typeid (X), ", Y = ", typeid (Y));
       assert (typeid (x) == typeid (Y));
    }

    runtest!(A, C); // pass
    runtest!(R, S); // pass
    runtest!(Q, S); // fail
    runtest!(Q, R); // would also fail
}
~~~

$ dmd -checkaction=context -unittest -main -run typeid
X = typeid.A, Y = typeid.C
X = typeid.R, Y = typeid.S
X = typeid.Q, Y = typeid.S
typeid.d(16): [unittest] typeid.Q != typeid.S
1/1 unittests FAILED

[1] https://dlang.org/spec/interface.html

Adam D. Ruppe <destructionator gmail.com> writes:

Interfaces always give their own typeid, this is because they 
might point to an object that doesn't have RTTI (though the 
compiler SHOULD be able to figure that out statically, it doesn't 
try).

To get the dynamic type, first cast it to Object, then type id.

typeid(cast(Object) o) is typeid(WhateverClass)