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Simplify is_string

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This commit is contained in:
Victor Zverovich 2019-06-05 08:41:00 -07:00
parent 388bb389e6
commit bae00aa8d7
1 changed files with 5 additions and 9 deletions
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14
include/fmt/core.h
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@ -392,19 +392,14 @@ FMT_CONSTEXPR basic_string_view<typename S::char_type> to_string_view(
}
namespace internal {
struct dummy_string_view {
using char_type = void;
};
dummy_string_view to_string_view(...);
void to_string_view(...);
using fmt::v5::to_string_view;
// Specifies whether S is a string type convertible to fmt::basic_string_view.
// It should be a constexpr function but MSVC 2017 fails to compile it in
// enable_if. MSVC 2015 fails to compile it as an alias template.
// enable_if and MSVC 2015 fails to compile it as an alias template.
template <typename S>
struct is_string
: bool_constant<
!std::is_empty<decltype(to_string_view(std::declval<S>()))>::value> {
struct is_string : std::is_class<decltype(to_string_view(std::declval<S>()))> {
};
struct error_handler {
@ -603,7 +598,8 @@ struct fallback_formatter {
"an operator<< that should be used");
};
template <typename S> struct char_t_impl {
template <typename S, typename = void> struct char_t_impl {};
template <typename S> struct char_t_impl<S, enable_if_t<is_string<S>::value>> {
typedef decltype(to_string_view(std::declval<S>())) result;
typedef typename result::char_type type;
};