"Interface method not implemented" if interface reflects on implementing class

[dlangBugzillaToGithub]

Simen Kjaeraas reported this on 2018-05-30T08:39:34Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=18915

Description

interface A
{
    import std.meta : AliasSeq;
    alias a = AliasSeq!(__traits(getMember, B, "foo"));
    void foo();
}

class B : A
{
    void foo() { }
}

Gives this error message:
Error: class `B` interface function void foo() is not implemented

[dlangBugzillaToGithub]

b2.temp commented on 2018-05-30T12:27:24Z

Is this supposed to work or is this a wrong diagnostic (type B not yet finished when used in A)

[dlangBugzillaToGithub]

simen.kjaras commented on 2018-05-31T06:31:19Z

I'd prefer it to work. This is essentially the use case:

interface A
{
    import std.traits;
    static foreach (e; __traits(derivedMembers, B)) {
        static foreach (fn; MemberFunctionsTuple!(B, e)) {
            mixin("@(__traits(getAttributes, fn)) ReturnType!fn "~e~"(Parameters!fn);");
        }
    }
}

class B : A
{
    void foo() { }
}

That is, we generate an interface based on a type, and derive that type from said interface. Since derivedMembers doesn't look at base classes and interfaces, this could possibly be made to work. 

Related forum discussion:
https://forum.dlang.org/post/dgzojfdiwsssflbnkwtk@forum.dlang.org