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15.3.12 Rust Format Strings ¶

Rust format strings are those supported by the formatx library https://crates.io/crates/formatx. These are those supported by the format! built-in https://doc.rust-lang.org/std/fmt/ with the restrictions listed in https://crates.io/crates/formatx, section "Limitations".

A Rust format string consists of

• an opening brace ‘{’,
• an optional non-empty sequence of digits or an optional identifier,
• optionally, a ‘:’ and a format specifier, where a format specifier is of the form [[fill]align][sign][#][0][minimumwidth][.precision][type] where
  • the fill character is any character,
  • the align flag is one of ‘<’, ‘>’, ‘^’,
  • the sign is one of ‘+’, ‘-’,
  • the # flag is ‘#’,
  • the 0 flag is ‘0’,
  • minimumwidth is a non-empty sequence of digits,
  • precision is a non-empty sequence of digits,
  • type is ‘?’,
• optional white-space,
• a closing brace ‘}’.

Brace characters ‘{’ and ‘}’ can be escaped by doubling them: ‘{{’ and ‘}}’.