allow format_as() to format reference #3739
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vitaut
requested changes
Dec 9, 2023
include/fmt/core.h
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| @@ -1332,7 +1332,7 @@ using ulong_type = conditional_t<long_short, unsigned, unsigned long long>; | |||
| template <typename T> struct format_as_result { | |||
| template <typename U, | |||
| FMT_ENABLE_IF(std::is_enum<U>::value || std::is_class<U>::value)> | |||
| static auto map(U*) -> decltype(format_as(std::declval<U>())); | |||
| static auto map(U*) -> typename std::decay<decltype(format_as(std::declval<U>()))>::type; | |||
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I think this should be remove_cvref_t and not decay.
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yes. it's a better fit in this case.
test/format-test.cc
Outdated
| struct struct_as_const_reference { | ||
| const std::string name = "foo"; | ||
| }; | ||
| auto format_as(const struct_as_const_reference& s) -> const std::string& { return s.name; } |
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v2:
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before this change, format_as() is unable to format a type which has `auto format_as() -> const another_type&`, and `another_type` is formattable. because `format_as_result` maps the result type as it is, and the compiler refuses to compile `static_cast<T*>(nullptr)`, where T is a reference type. but it would be handy if we could use `format_as()` to format types which, for instance, owns / inherit from a formattable type, and delegate the formatter to these variables instead without creating a copy of them. in this change: * instruct `format_as_result` to map the result type to the decayed type, so that `type` can be the decayed type of result type, and this also enables `type` to be formattable, as long as the decayed type is formattable. * corresponding test is added to format-test.cc Signed-off-by: Kefu Chai <tchaikov@gmail.com>
vitaut
approved these changes
Dec 10, 2023
|
Merged, thanks! |
happymonkey1
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to happymonkey1/fmt
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this pull request
Apr 7, 2024
before this change, format_as() is unable to format a type which has `auto format_as() -> const another_type&`, and `another_type` is formattable. because `format_as_result` maps the result type as it is, and the compiler refuses to compile `static_cast<T*>(nullptr)`, where T is a reference type. but it would be handy if we could use `format_as()` to format types which, for instance, owns / inherit from a formattable type, and delegate the formatter to these variables instead without creating a copy of them. in this change: * instruct `format_as_result` to map the result type to the decayed type, so that `type` can be the decayed type of result type, and this also enables `type` to be formattable, as long as the decayed type is formattable. * corresponding test is added to format-test.cc Signed-off-by: Kefu Chai <tchaikov@gmail.com>
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before this change, format_as() is unable to format a type which has
auto format_as() -> const another_type&, andanother_typeis formattable. becauseformat_as_resultmaps the result type as it is, and the compiler refuses to compilestatic_cast<T*>(nullptr), where T is a reference type. but it would be handy if we could useformat_as()to format types which, for instance, owns / inherit from a formattable type, and delegate the formatter to these variables instead without creating a copy of them.in this change:
format_as_resultto map the result type to the decayed type, so thattypecan be the decayed type of result type, and this also enablestypeto be formattable, as long as the decayed type is formattable.