[Bug libstdc++/81263] Work around CWG issue 1558 (guarantee SFINAE when using `void_t`)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81263 Jonathan Wakely changed: What|Removed |Added Status|UNCONFIRMED |RESOLVED Resolution|--- |INVALID --- Comment #3 from Jonathan Wakely --- CWG 1558 was implemented in GCC ages ago (though given that you haven't said what version you're using, maybe it isn't for you). This is not a library bug though, it's a limitation of void_t and the current core language.
[Bug libstdc++/81263] Work around CWG issue 1558 (guarantee SFINAE when using `void_t`)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81263
TC changed:
What|Removed |Added
CC||rs2740 at gmail dot com
--- Comment #2 from TC ---
This is not DR1558; the issue here is declaration matching rather than SFINAE.
Just having the two func definitions is sufficient to trigger the error:
template using void_t = void;
template * = nullptr>
void func() {}
template * = nullptr>
void func() {}
This is actually CWG 1980.
[Bug libstdc++/81263] Work around CWG issue 1558 (guarantee SFINAE when using `void_t`)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81263 W E Brown changed: What|Removed |Added CC||webrown.cpp at gmail dot com --- Comment #1 from W E Brown --- I have not confirmed the report but, as the originator of the void_t technique, I do have a few comments: a) The cited CWG issue was resolved several years ago, and is in DR status. That means the exhibited code is expected to work. If it doesn't, I consider it a compiler issue, not a library issue. b) Therefore, once the compiler is fixed (if necessary), ISTM there should be no reason to use the cited alternative definition of void_t, which I first discovered and disseminated as a temporary workaround only. See my WG21 paper N3911 and/or part 2 of my metaprogramming talk at CppCon 2014. c) FWIW, while it should work as exhibited in the report, the code does not quite conform to the design of the detection idiom. I prefer to write such a 2nd template parameter as a type parameter of the form class = void_t.
