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Improve handling of unformattable args

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This commit is contained in:
Victor Zverovich
2024-09-16 18:52:18 -07:00
parent 527e98e3f8
commit 4197727712
2 changed files with 19 additions and 20 deletions
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37
include/fmt/base.h
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@ -1123,8 +1123,14 @@ constexpr auto has_const_formatter() -> bool {
return has_const_formatter_impl<Char>(static_cast<T*>(nullptr));
}
// Maps formatting argument types to a smaller set. Returns void on
// errors to be SFINAE-friendly.
template <typename T, typename Char, typename U = remove_const_t<T>>
struct formattable
: bool_constant<has_const_formatter<U, Char>() ||
(std::is_constructible<formatter<U, Char>>::value &&
!std::is_const<T>::value)> {};
// Maps formatting argument types to natively supported types or user-defined
// types with formatters. Returns void on errors to be SFINAE-friendly.
template <typename Char> struct type_mapper {
static auto map(signed char) -> int;
static auto map(unsigned char) -> unsigned;
@ -1176,14 +1182,8 @@ template <typename Char> struct type_mapper {
template <typename T, FMT_ENABLE_IF(use_format_as<T>::value)>
static auto map(const T& x) -> decltype(map(format_as(x)));
template <typename T, typename U = remove_const_t<T>>
struct formattable
: bool_constant<has_const_formatter<U, Char>() ||
(std::is_constructible<formatter<U, Char>>::value &&
!std::is_const<T>::value)> {};
template <typename T, FMT_ENABLE_IF(use_formatter<remove_const_t<T>>::value)>
static auto map(T&) -> conditional_t<formattable<T>::value, T&, void>;
static auto map(T&) -> conditional_t<formattable<T, Char>::value, T&, void>;
template <typename T, FMT_ENABLE_IF(is_named_arg<T>::value)>
static auto map(const T& named_arg) -> decltype(map(named_arg.value));
@ -2192,23 +2192,15 @@ template <typename Context> class value {
: named_args{args, size} {}
private:
template <typename T> FMT_CONSTEXPR value(const T& x, custom_tag) {
template <typename T, FMT_ENABLE_IF(formattable<T, char_type>::value)>
FMT_CONSTEXPR value(const T& x, custom_tag) {
using value_type = remove_cvref_t<T>;
enum { formattable = !std::is_same<T, void>::value };
#if defined(__cpp_if_constexpr)
if constexpr (!formattable) type_is_unformattable_for<T, char_type> _;
// T may overload operator& e.g. std::vector<bool>::reference in libc++.
if constexpr (std::is_same<decltype(&x), remove_reference_t<T>*>::value)
custom.value = const_cast<value_type*>(&x);
#endif
static_assert(
formattable,
"cannot format an argument; to make type T formattable provide a "
"formatter<T> specialization: https://fmt.dev/latest/api.html#udt");
custom.value = nullptr;
if (!is_constant_evaluated())
custom.value =
@ -2216,6 +2208,13 @@ template <typename Context> class value {
custom.format = format_custom<value_type, formatter<value_type, char_type>>;
}
template <typename T, FMT_ENABLE_IF(!formattable<T, char_type>::value)>
FMT_CONSTEXPR value(const T&, custom_tag) {
// Cannot format an argument; to make type T formattable provide a
// formatter<T> specialization: https://fmt.dev/latest/api.html#udt.
type_is_unformattable_for<T, char_type> _;
}
// Formats an argument of a custom type, such as a user-defined class.
template <typename T, typename Formatter>
static void format_custom(void* arg, parse_context<char_type>& parse_ctx,

2
include/fmt/format.h
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@ -779,7 +779,7 @@ using is_integer =
#if FMT_USE_FLOAT128
using float128 = __float128;
#else
using float128 = void;
struct float128 {};
#endif
template <typename T> using is_float128 = std::is_same<T, float128>;