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Bug 19906 – __traits(isRef) always yields false for auto ref parameter

Status: RESOLVED
Resolution: INVALID
Severity: normal
Priority: P1
Component: dmd
Product: D
Version: D2
Platform: All
OS: All
Creation time: 2019-05-27T22:00:09Z
Last change time: 2019-05-28T04:43:05Z
Assigned to: No Owner
Creator: Andrei Alexandrescu

Comments

Comment #0 by andrei — 2019-05-27T22:00:09Z

Consider: import std.stdio; void fun(T)(auto ref T x) { pragma(msg, __PRETTY_FUNCTION__); static if (is(__traits(isRef, x))) { writeln("ref: ", x); } else { writeln("non ref: ", x); } } void main() { int a; fun(a); fun(42); } This prints: void onlineapp.fun!int.fun(ref int x) void onlineapp.fun!int.fun(int x) non ref: 0 non ref: 42 It should print: void onlineapp.fun!int.fun(ref int x) void onlineapp.fun!int.fun(int x) ref: 0 non ref: 42

Comment #1 by turkeyman — 2019-05-28T00:03:56Z

Oh wow... isRef is unreliable? I probably have *SO MUCH* broken code >_<

Comment #2 by sprink.noreply — 2019-05-28T00:33:26Z

The issue here is specifically with is(). __traits(isRef, x) produces the correct value and works correctly if you remove is().

Comment #3 by sprink.noreply — 2019-05-28T00:41:21Z

Just to clarify the logic would still be incorrect. It would always be true unless there was some kind of error in __traits().

Comment #4 by turkeyman — 2019-05-28T00:42:57Z

I suspect the `is` was an accident.

Comment #5 by turkeyman — 2019-05-28T00:44:11Z

Which is relieving, I was worried for a second there!

Comment #6 by andrei — 2019-05-28T04:43:05Z

Oops, my bad. Apologies.