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Report unformattable type name more prominently

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This commit is contained in:
Victor Zverovich 2020-07-13 08:46:53 -07:00
parent 8fa20b471b
commit 0097cf113d
1 changed files with 18 additions and 10 deletions
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28
include/fmt/core.h
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@ -973,6 +973,8 @@ enum { long_short = sizeof(long) == sizeof(int) };
using long_type = conditional_t<long_short, int, long long>;
using ulong_type = conditional_t<long_short, unsigned, unsigned long long>;
struct unformattable {};
// Maps formatting arguments to core types.
template <typename Context> struct arg_mapper {
using char_type = typename Context::char_type;
@ -1081,15 +1083,7 @@ template <typename Context> struct arg_mapper {
return map(val.value);
}
int map(...) {
constexpr bool formattable = sizeof(Context) == 0;
static_assert(
formattable,
"Cannot format argument. To make type T formattable provide a "
"formatter<T> specialization: "
"https://fmt.dev/latest/api.html#formatting-user-defined-types");
return 0;
}
unformattable map(...) { return {}; }
};
// A type constant after applying arg_mapper<Context>.
@ -1264,13 +1258,27 @@ FMT_CONSTEXPR basic_format_arg<Context> make_arg(const T& value) {
return arg;
}
template <typename T> struct formattable : std::false_type {};
template <typename T> int check(unformattable) {
static_assert(
formattable<T>(),
"Cannot format argument. To make type T formattable provide a "
"formatter<T> specialization: "
"https://fmt.dev/latest/api.html#formatting-user-defined-types");
return 0;
}
template <typename T, typename U> inline const U& check(const U& val) {
return val;
}
// The type template parameter is there to avoid an ODR violation when using
// a fallback formatter in one translation unit and an implicit conversion in
// another (not recommended).
template <bool IS_PACKED, typename Context, type, typename T,
FMT_ENABLE_IF(IS_PACKED)>
inline value<Context> make_arg(const T& val) {
return arg_mapper<Context>().map(val);
return check<T>(arg_mapper<Context>().map(val));
}
template <bool IS_PACKED, typename Context, type, typename T,