Fix for issue 8589 was incomplete. --- void f(int[int] function() del) { assert(!del()); } typeof(null) g() { return null; } void main() { f(&g); f(() => null); } --- As typeof(null) is a pointer type, whilst associative arrays are value types. So can't possibly be covariant.
It seems that the got auto-resolved without linking a reference to the PR nor commit. https://github.com/dlang/dmd/pull/9272
dlang/dmd pull request #9435 "[dmd-cxx] fix Issue 19618 - Associative arrays are not covariant with typeof(null)" was merged into dmd-cxx: - c9d1c94080a5fc233ce4bdf9ebd3f07ba224e9dd by Iain Buclaw: fix Issue 19618 - Associative arrays are not covariant with typeof(null) As associative arrays are value types (`struct {void*}`), which are passed and returned differently to the void pointer typeof(null). https://github.com/dlang/dmd/pull/9435