Bug 14941 – dmd rejects op assignment to opIndex expression

Found by Ryuichi OHORI, see issue 14935. ---- struct V { void opOpAssign(string op)(int x) {} } struct S { V opIndex() {return V();} } void main() { S s; auto v = s[]; v += 2; /* no error */ s.opIndex() += 2; /* no error */ s[] += 2; /* Error: S cannot be sliced with [] */ } ---- Clearly, S can be sliced with []. And a V can be add-assigned. The compiler seems to give up when there's opIndexOpAssign for S, but it should try opIndex+opOpAssign, too. Also fails in the same manner when S.opIndex returns e.g. `ref int`. If nothing else, the error message should be improved.

*** This issue has been marked as a duplicate of issue 14624 ***