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Use type_identity to block unnecessary template argument deduction (thanks Tim Song)

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This commit is contained in:
Victor Zverovich
2020-01-15 08:09:48 -08:00
parent 4bbe57cebf
commit c8dd9cc99d
7 changed files with 65 additions and 46 deletions
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28
include/fmt/core.h
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@@ -217,7 +217,7 @@
FMT_BEGIN_NAMESPACE
// Implementations of enable_if_t and other metafunctions for pre-C++14 systems.
// Implementations of enable_if_t and other metafunctions for older systems.
template <bool B, class T = void>
using enable_if_t = typename std::enable_if<B, T>::type;
template <bool B, class T, class F>
@@ -229,6 +229,8 @@ template <typename T>
using remove_const_t = typename std::remove_const<T>::type;
template <typename T>
using remove_cvref_t = typename std::remove_cv<remove_reference_t<T>>::type;
template <typename T> struct type_identity { using type = T; };
template <typename T> using type_identity_t = typename type_identity<T>::type;
struct monostate {};
@@ -1220,7 +1222,13 @@ using wformat_context = buffer_context<wchar_t>;
such as `~fmt::vformat`.
\endrst
*/
template <typename Context, typename... Args> class format_arg_store {
template <typename Context, typename... Args>
class format_arg_store
#if FMT_GCC_VERSION < 409
// Workaround a GCC template argument substitution bug.
: public basic_format_args<Context>
#endif
{
private:
static const size_t num_args = sizeof...(Args);
static const bool is_packed = num_args < internal::max_packed_args;
@@ -1239,7 +1247,12 @@ template <typename Context, typename... Args> class format_arg_store {
: internal::is_unpacked_bit | num_args;
format_arg_store(const Args&... args)
: data_{internal::make_arg<is_packed, Context>(args)...} {}
:
#if FMT_GCC_VERSION < 409
basic_format_args<Context>(*this),
#endif
data_{internal::make_arg<is_packed, Context>(args)...} {
}
};
/**
@@ -1426,9 +1439,10 @@ template <typename... Args, typename S, typename Char = char_t<S>>
inline format_arg_store<buffer_context<Char>, remove_reference_t<Args>...>
make_args_checked(const S& format_str,
const remove_reference_t<Args>&... args) {
static_assert(all_true<(!std::is_base_of<view, remove_reference_t<Args>>::value ||
!std::is_reference<Args>::value)...>::value,
"passing views as lvalues is disallowed");
static_assert(
all_true<(!std::is_base_of<view, remove_reference_t<Args>>::value ||
!std::is_reference<Args>::value)...>::value,
"passing views as lvalues is disallowed");
check_format_string<remove_const_t<remove_reference_t<Args>>...>(format_str);
return {args...};
}
@@ -1440,7 +1454,7 @@ std::basic_string<Char> vformat(basic_string_view<Char> format_str,
template <typename Char>
typename buffer_context<Char>::iterator vformat_to(
buffer<Char>& buf, basic_string_view<Char> format_str,
basic_format_args<buffer_context<Char>> args);
basic_format_args<buffer_context<type_identity_t<Char>>> args);
FMT_API void vprint_mojibake(std::FILE*, string_view, format_args);
} // namespace internal