C++ named requirements: BasicFormatter (od C++20)
BasicFormatter is a type that abstracts formatting operations for a given formatting argument type and character type. Specializations of std::formatter are required to meet the requirements of BasicFormatter.
A BasicFormatter is a Formatter if it is able to format both const and non-const arguments.
Requirements
A type satisfies BasicFormatter if it is semiregular, meaning it satisfies:
And, given
Arg
, a formatting argument typeCharT
, a character typeBasicFormatter
, a BasicFormatter type for types Arg and CharTOutputIt
, a LegacyOutputIterator typef
, a value of type (possibly const) BasicFormatterg
, a value of type BasicFormatterarg
, an lvalue of type ArgParseContext
, an alias ofstd::basic_format_parse_context<CharT>
FormatContext
, an alias ofstd::basic_format_context<OutputIt, CharT>
parse_ctx
, an lvalue of type ParseContextformat_ctx
, an lvalue of type FormatContext
Expression | Return type | Semantics |
---|---|---|
g.parse(parse_ctx) | ParseContext::iterator | * Parses the format-spec [parse_ctx.begin(), parse_ctx.end()) for type Arg until the first unmatched character. * Throws [std::format_error] unless the whole range is parsed or the unmatched character is } . [1] * Stores the parsed format specifiers in g and returns an end iterator of the parsed range. |
f.format(arg, format_ctx) | FormatContext::iterator | * Formats arg 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 * arg, * 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. |
1 ↑ This allows formatters to emit meaningful error messages.