https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94721
Bug ID: 94721
Summary: C++2a: Three-way comparison operator for function
pointers rejected
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: daniel.kruegler at googlemail dot com
Target Milestone: ---
Using the compiler flags
-Wall -Wextra -std=c++2a -pedantic
the following code example
//------------------
#include <compare>
void foo() {}
void bar() {}
int main()
{
auto p1 = &foo;
auto p2 = &bar;
return (p1 <=> p2) != 0 ? 0 : 1;
}
//------------------
is rejected:
>>>>>>>>>>>>>>>
prog.cc: In function 'int main()':
prog.cc:10:14: error: invalid operands of types 'void (*)()' and 'void (*)()'
to binary 'operator<=>'
10 | return (p1 <=> p2) != 0 ? 0 : 1;
| ~~ ^~~ ~~
| | |
| | void (*)()
| void (*)()
<<<<<<<<<<<<<<<
This code should be accepted, because according to [over.built] p18:
"For every T, where T is [..] a pointer type, there exist candidate operator
functions of the form
[..]
R operator<=>(T, T);
where R is the result type specified in 7.6.8."
And 7.6.8 [expr.spaceship] p7 says:
"[..] If two pointer operands p and q compare equal (7.6.10), p <=> q yields
std::strong_ordering::equal; if p and q compare unequal, p <=> q yields
std::strong_ordering::less if q compares greater than p and
std::strong_ordering::greater if p compares greater than q (7.6.9). Otherwise,
the result is unspecified."
