Problem found on tuples by Magnus Lie Hetland, then reduced:


import std.typecons;
void main() {
    alias Tuple!int T;
    const T t;
    bool b = t == t;
}


DMD 2.052 shows:

test.d(5): Error: template std.typecons.Tuple!(int).Tuple.opEquals(R) if (isTuple!(R)) does not match any function template declaration
test.d(5): Error: template std.typecons.Tuple!(int).Tuple.opEquals(R) if (isTuple!(R)) cannot deduce template function from argument types !()(const(Tuple!(int)))



I think it can be further reduced to:

struct Foo(T) {
    bool opEquals(R)(R rhs) {
        return false;
    }
}
void main() {
    const Foo!int f;
    bool result = f == f;
}