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// { dg-options "-std=gnu++23" }
// { dg-do compile { target c++23 } }
#include <format>
struct S { };
template<> struct std::formatter<S> : std::formatter<const char*> {
template<class Out>
auto format(S, std::basic_format_context<Out, char>& ctx) const {
return formatter<const char*>::format("ess", ctx);
}
};
struct T { };
template<> struct std::formatter<T> : std::formatter<const char*> {
// This function only accepts std::format_context, not other contexts.
auto format(T, std::format_context& ctx) const {
return formatter<const char*>::format("tee", ctx);
}
};
struct U { };
void
test_concept() // [format.formattable]
{
static_assert( std::formattable<int, char> );
static_assert( std::formattable<const int, char> );
static_assert( std::formattable<int, wchar_t> );
static_assert( std::formattable<const int, wchar_t> );
static_assert( std::formattable<char, char> );
static_assert( std::formattable<char*, char> );
static_assert( std::formattable<wchar_t, wchar_t> );
static_assert( std::formattable<wchar_t*, wchar_t> );
static_assert( std::formattable<char, wchar_t> );
static_assert( ! std::formattable<char*, wchar_t> );
static_assert( ! std::formattable<wchar_t, char> );
static_assert( ! std::formattable<wchar_t*, char> );
static_assert( std::formattable<S, char> );
static_assert( std::formattable<const S, char> );
static_assert( ! std::formattable<S, wchar_t> ); // only formats as char
static_assert( ! std::formattable<T, char> ); // formatter not generic
static_assert( ! std::formattable<U, char> ); // no formatter
}
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