[Bug libstdc++/110138] Extra constructor called when using basic_string::operator+

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110138

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
What matters is the "value" of the allocator, not how many times it gets
copied.