https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109876
Bug ID: 109876
Summary: initializer_list not usable in constant expressions in
a template
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: barry.revzin at gmail dot com
Target Milestone: ---
Consider this example:
#include <initializer_list>
template <int S>
struct Array {
};
#ifdef USE_TEMPLATE
template <int N>
#endif
struct Foo
{
static constexpr std::initializer_list<int> num = { 1, 2 };
Array<num.size()> ctx;
};
#ifdef USE_TEMPLATE
void f(Foo<5>) { }
#else
void f(Foo) { }
#endif
In all recent versions of gcc, compiling with -DUSE_TEMPLATE fails with an
error like:
<source>:15:17: in 'constexpr' expansion of
'Foo<N>::num.std::initializer_list<int>::size()'
<source>:15:19: error: the value of 'Foo<N>::num' is not usable in a constant
expression
15 | Array<num.size()> ctx;
| ^
This used to work in gcc 7 and gcc 8 (except 8.1), and I don't think there's
anything about Foo being a template that should prevent this from working. The
non-template case works on all gcc versions I've tried.
