Bug 3278 – Empty tuples don't match

A tuple containing an empty tuple is not the same as an empty tuple and two such beasts are considered incompatible. ---- import std.typetuple; template TypeList(T...) { alias T toTuple; } static assert (TypeList!().toTuple == TypeTuple!()); ---- Error: incompatible types for ((()) == (())): '()' and '()'

Reduced testcase: template TypeTuple(TList...) { alias TList TypeTuple; } template TypeList(T...) { alias T toTuple; } static assert (TypeList!().toTuple == TypeTuple!()); Actually dmd is right to reject the code, but it's bad at conveying the reason. You're trying to compare types with a '==' expression directly, which is not allowed. Use is(A==B), instead, where A,B are types (documented), or type-tuples (I think that it works for type-tuples is undocumented, but type-tuples are treated like types in the frontend). These asserts compile and the tests pass: static assert (is(TypeList!().toTuple == TypeTuple!())); static assert (is(TypeList!(int).toTuple == TypeTuple!(int))); You can see it has nothing to do with empty tuples being a special case or so. But I would like dmd to produce an error message like this: Error: can not compare types with '==', use is(TypeA==TypeB) instead I changed importance to normal, because it's just a bad error message. I see you have wrong-code in the keywords list, so maybe you knew that already?

*** This issue has been marked as a duplicate of issue 3279 ***