std::formattable - cppreference.com
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    std::formattable

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    C++
     
    Text processing library
     
    Formatting library
    Standard format specification
    Formatting functions
    (C++20)
    (C++20)
    (C++20)
    (C++20)
    (C++20)
    (C++20)
    Format strings
    (C++20)(C++20)(C++20)
    (C++26)
    Formatting concepts
    (C++23)
    Formatter
    (C++20)
    (C++23)
    (C++23)
    (C++23)
    (C++23)
    (C++20)(C++20)(C++20)
    (C++20)(C++20)(C++20)
    (C++23)
    (C++23)
    Formatting arguments
    (C++20)
    (C++20)
    (C++20)(C++20)(C++20)
    (C++20) (deprecated in C++26)
    (C++20)(C++20)
    Format error
    (C++20)
     
    Defined in header <format> 
    template< class T, class CharT >
concept formattable = /* formattable_with */<
  std::remove_reference_t<T>,
  std::basic_format_context</* fmt_iter_for */<CharT>, CharT>
>;
    		(1) (since C++23)
    Helper templates
    		 
    template< class CharT >
using /* fmt_iter_for */ = /* unspecified */;
    		(2) (exposition only*) 
    template< class T, class Context, 
          class Formatter =
              typename Context::template
                  formatter_type<std::remove_const_t<T>> >
concept /* formattable_with */ = 
  std::semiregular<Formatter> &&
  requires (Formatter& f, const Formatter& cf, T&& t, Context fc, 
            std::basic_format_parse_context<
                typename Context::char_type
            > pc) {
    { f.parse(pc) } -> std::same_as<typename decltype(pc)::iterator>;
    { cf.format(t, fc) } -> std::same_as<typename Context::iterator>;
  };
    		(3) (exposition only*)

    The concept formattable specifies that std::formatter<std::remove_cvref_t<T>, CharT> meets the requirements of BasicFormatter and Formatter (if std::remove_reference_t<T> is const-qualified).

    The exposition-only alias template /* fmt_iter_for */ yields an unspecified type that satisfies std::output_iterator<const CharT&>.

    Defect reports

    The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

    DR Applied to Behavior as published Correct behavior
    LWG 3925 C++23 the second template argument of std::basic_format_context was not provided provided

    See also