On 12/05/21 12:58 +0300, Antony Polukhin wrote:
ср, 12 мая 2021 г. в 12:18, Jonathan Wakely <jwak...@redhat.com>:
<...>
Or just leave it undefined, as libc++ seems to do according to your
comment in PR 89728:
error: implicit instantiation of undefined template
'std::__1::ctype<std::__1::basic_string<char> >'
Was your aim to have a static_assert that gives a more descriptive
error? We could leave it undefined in C++98 and have the static assert
for C++11 and up.
Leaving it undefined would be the best. It would allow SFINAE on ctype
and a compile time error is informative enough.
However, there may be users who instantiate ctype<ThierChar> in a
shared library without ctype<ThierChar> template specializations in
the main executable. Making the default ctype undefined would break
their compilation:
#include <locale>
// no ctype<ThierChar> specialization
c = std::tolower(ThierChar{42}, locale_from_shared_library()); // OK
right now in libstdc++, fails on libc++
What I meant was leaving the partial specialization undefined, not the
primary template, i.e.
--- a/libstdc++-v3/include/bits/locale_facets.h
+++ b/libstdc++-v3/include/bits/locale_facets.h
@@ -1476,6 +1476,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
};
#endif //_GLIBCXX_USE_WCHAR_T
+ template<typename _CharT, typename _Traits, typename _Alloc>
+ class ctype<basic_string<_CharT, _Traits, _Alloc> >;
+
/// class ctype_byname [22.2.1.2].
template<typename _CharT>
class ctype_byname : public ctype<_CharT>
This makes your test fail with errors like this:
In file included from /home/jwakely/gcc/12/include/c++/12.0.0/locale:40,
from loc.C:1:
/home/jwakely/gcc/12/include/c++/12.0.0/bits/locale_facets.h: In instantiation of 'bool
std::isspace(_CharT, const std::locale&) [with _CharT =
std::__cxx11::basic_string<char>]':
loc.C:16:15: required from here
/home/jwakely/gcc/12/include/c++/12.0.0/bits/locale_facets.h:2600:47: error: invalid use of
incomplete type 'const class std::ctype<std::__cxx11::basic_string<char> >'
2600 | { return use_facet<ctype<_CharT> >(__loc).is(ctype_base::space,
__c); }
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
But it shouldn't affect the uses of ctype<TheirChar>.
What do you think?
