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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/94003] is_constructible seems to have sideeffects
Date: Wed, 11 Mar 2020 18:39:43 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94003

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Depends on|                            |41437

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Almost certainly due to one of the bugs linked to PR 59002, probably PR 414=
37.

Inside the function template access checking doesn't work properly, so you =
can
use the private constructor, and the first instantiation of the trait gives=
 the
wrong answer:

template <typename X> static bool why() {
  Class c;
  return std::is_constructible<Class>::value;
}

Then when the trait is rechecked later it has already been instantiated, an=
d so
continues to give the wrong answer.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D41437
[Bug 41437] No access control for classes in template functions=