https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116217
Bug ID: 116217
Summary: RangeAdaptorClosure pipe operator is underconstrained
Product: gcc
Version: 14.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: eddiejnolan at gmail dot com
Target Milestone: ---
libstdc++ accepts the following, which is rejected by libc++ and MSVC:
#include <ranges>
struct foo : std::ranges::range_adaptor_closure<foo> {
auto operator()(auto const&) const {
return std::ranges::empty_view<int>{};
}
};
inline constexpr foo bar;
int main() {
auto quux{0 | bar};
}
Compiler explorer link: https://godbolt.org/z/ssjqqKbzb
The other standard libraries both check that the parameter passed to the range
adaptor closure satisifies the range concept, as specified in the wording
(https://eel.is/c++draft/range.adaptor.object):
A range adaptor closure object is a unary function object that accepts a range
argument.
For a range adaptor closure object C and an expression R such that
decltype((R)) models range, the following expressions are equivalent:
C(R)
R | C
libstdc++ doesn't check that the parameter models range, only checking that the
range adaptor closure object is invocable with that parameter.
