https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102589
Bug ID: 102589
Summary: spaceship: std::map does not use specialised operator<
for value
Product: gcc
Version: 11.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: gjasny at googlemail dot com
Target Milestone: ---
Created attachment 51546
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51546&action=edit
Testcase
Hello,
I stumbled over this issue when porting a code base from C++17 to C++20. Both:
GNU libstdc++ as well as MSVC STL show the unexpected behaviour. Libc++ seems
to do the right thing.
Describe the bug
Compiling the test case with C++17 works as expected whereas compiling it with
C++20 makes the test assumption fail.
The reason is that for C++ 20 builds the specialised operator<(const FooPtr&
left, const FooPtr& right) is not picked up. Instead the default operator<=>
for std::shared_ptr is used which only compares the raw pointers and not the
content they point to.
Expected behavior
I'd expect that with C++17 and C++20 the STL would prefer the specialised
operator<(const FooPtr& left, const FooPtr& right) over the synthesised <=>
one. That would also align with the strong backwards compatibilities C++
strives for.
GCC version
g++-11 (Debian 11.2.0-8) 11.2.0
Links
Microsoft STL Issue: https://github.com/microsoft/STL/issues/2234
Debian Sid based reproducer: https://github.com/gjasny/map-spaceship-testcase
Godbolt: https://godbolt.org/z/objPnjo84
Thanks,
Gregor
