[Bug libstdc++/95245] std::sort copies custom comparator

2020-05-20 Thread redi at gcc dot gnu.org 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95245

Jonathan Wakely  changed:

   What|Removed |Added

 Status|UNCONFIRMED |NEW
   Last reconfirmed||2020-05-20
 Ever confirmed|0   |1
   Keywords||missed-optimization

--- Comment #2 from Jonathan Wakely  ---
I think other implementations automatically wrap the function in a
reference-like type.

See PR 51965 for similar issues with other recursively-defined algorithms.

N.B. GCC 7 is no longer supported or maintained, so bug reports should be for
currently-supported versions.

[Bug libstdc++/95245] std::sort copies custom comparator

2020-05-20 Thread redi at gcc dot gnu.org 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95245

--- Comment #1 from Jonathan Wakely  ---
[algorithms.requirements] paragraph 10 says:

[Note: Unless otherwise specified, algorithms that take function objects as
arguments are permitted to copy those function objects freely. Programmers for
whom object identity is important should consider using a wrapper class that
points to a noncopied implementation object such as reference_wrapper 
20.14.5), or some equivalent solution. — end note]