mixin templates and classes

[Denis Shelomovskij]

IMHO this should compile:

---
mixin template T() { final void f() { } }

class A { mixin T ta; }
class B : A { mixin T tb; }
---

these asserts should pass:

---
mixin template T(string s) {
     string f() { return s; }
}

class A {
     mixin T!"T1" ta1;
     mixin T!"T2" ta2;
     mixin T!"T";
}

class B : A {
     override string f() { return "B"; }
}

void main() {
     assert((new B).f() == "B");
     assert((new B).ta1.f() == "T1"); // Fails: ta1.f() = "B"
     assert((new B).ta2.f() == "T2");

     // Doesn't compile because of Issue 8033
     // Will fail once will compile: (new A).f() = "T"
//  assert((new A).f() == "B");
}
---

and this should not compile (Issue 8034):

---
mixin template T(string s) {
     string f() { return s; }
}

class A {
     mixin T!"T1" ta1;
     mixin T!"T2" ta2;
}

class B : A {
     override string f() { return "B"; }
}
---

And I see one easy way to improve the situation: disallow named template 
mixins to override/add virtual methods except a destructor.

Thoughts?

-- 
Денис В. Шеломовский
Denis V. Shelomovskij