https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93480
Will Wray <wjwray at gmail dot com> changed:
What |Removed |Added
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CC| |wjwray at gmail dot com
--- Comment #1 from Will Wray <wjwray at gmail dot com> ---
I'm keen to see this fixed (and open to contribute)
(defaulted array comparison now works on Clang & MSVC).
Workaround for lack of compiler-generated array<=>array
is awkward and brittle: https://godbolt.org/z/xr668E
* Preprocessor conditional compilation is required
(at least there seems no way to detect array<=>array
support and dispatch to a user-defined comparison
only as needed - iff array members are present):
# if ! defined(__GNUC__) || defined(__clang__)
auto operator<=>(C const&) const = default;
# else
constexpr auto operator<=>(C const& r) const {
return three_way_compare(x,r.x);
}
#endif
Then:
* A generic 3-way comparison for array should be recursive.
* Achieving efficient/vector codegen is not straightforward.
* Deducing the return type is subtle:
template <typename E, int N>
constexpr auto three_way_compare(E const(&l)[N],
E const(&r)[N]) {
auto c = l[0] <=> r[0];
for (int i = 0; ++i != N; c = l[i] <=> r[i])
if (c != 0)
return c;
return c;
}
So it'd be better for all if this were compiler-generated.
