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C++ named requirements: Formatter (since C++20)

Formatter is a type that abstracts formatting operations for a given formatting argument type and character type. Specializations of std::formatter provided by the standard library are required to meet the requirements of Formatter except as noted otherwise.

A Formatter is able to format both const and non-const arguments, typically by providing a format member function that takes a const reference.

Requirements​

A type satisfies Formatter if it satisfies BasicFormatter and given

  • Arg, a formatting argument type
  • CharT, a character type
  • Formatter, a Formatter type for types Arg and CharT
  • OutputIt, a LegacyOutputIterator type
  • f, a value of type (possibly const) Formatter
  • g, a value of type Formatter
  • arg, an lvalue of type Arg
  • t, a value of type convertible to (possibly const) Arg
  • ParseContext, an alias of std::basic_format_parse_context<CharT>
  • FormatContext, an alias of std::basic_format_context<OutputIt, CharT>
  • parse_ctx, an lvalue of type ParseContext
  • format_ctx, an lvalue of type FormatContext
ExpressionReturn typeSemantics
f.format(t, format_ctx)FormatContext::iterator* Formats t according to the specifiers stored in f, writes the output to format_ctx.out() and returns an end iterator of the output range.
* The output shall only depend on
  * t,
  * format_ctx.locale(),
  * the range [parse_ctx.begin(), parse_ctx.end()) from the last call to
   f.parse(parse_ctx), and
  * format_ctx.arg(n) for any value n of type std::size_t.
f.format(arg, format_ctx)FormatContext::iteratorAs above, but does not modify arg.