digitalmars.D.bugs - [Issue 15231] New: opOpAssign allows assignment to rvalue
- via Digitalmars-d-bugs (44/44) Oct 21 2015 https://issues.dlang.org/show_bug.cgi?id=15231
https://issues.dlang.org/show_bug.cgi?id=15231 Issue ID: 15231 Summary: opOpAssign allows assignment to rvalue Product: D Version: D2 Hardware: x86_64 OS: Linux Status: NEW Severity: enhancement Priority: P1 Component: dmd Assignee: nobody puremagic.com Reporter: ryan rcorre.net unittest { struct MyInt { int _val; auto opBinary(string op)(int other) { return mixin("_val"~op~"other"); } void opOpAssign(string op)(int other) { _val = mixin("_val"~op~"other"); } } struct Foo { int _i; MyInt _mi; auto i() { return _i; } auto mi() { return _mi; } auto i(int val) { return _i = val; } auto mi(int val) { return _mi = MyInt(val); } } auto f = Foo(1, MyInt(1)); static assert(!__traits(compiles, f.i += 1)); // f.i is an rvalue static assert(!__traits(compiles, f.mi += 1)); // f.mi should be an rvalue } The final assert fails.f.mi is not an lvalue, and therefore f.mi += 1 should not compile. It deceptively appears to increment `mi` while truly doing nothing. The compiler disallows this for builtin types (e.g. int) but somehow the use of opOpAssign bypasses this check. Ideally, I'd love to have support for in-place property modification (https://issues.dlang.org/show_bug.cgi?id=8006), but failing that, I think this should be disallowed to avoid confusion. P.S. not sure whether this belongs in DMD or druntime --
Oct 21 2015