format in std - Rust (original) (raw)
Macro std::format
macro_rules! format {
($($arg:tt)*) => { ... };
}Expand description
Creates a String using interpolation of runtime expressions.
The first argument format! receives is a format string. This must be a string literal. The power of the formatting string is in the {}s contained.
Additional parameters passed to format! replace the {}s within the formatting string in the order given unless named or positional parameters are used; see std::fmt for more information.
A common use for format! is concatenation and interpolation of strings. The same convention is used with print! and write! macros, depending on the intended destination of the string.
To convert a single value to a string, use the to_string method. This will use the Display formatting trait.
format! panics if a formatting trait implementation returns an error. This indicates an incorrect implementation since fmt::Write for String never returns an error itself.
format!("test");
format!("hello {}", "world!");
format!("x = {}, y = {y}", 10, y = 30);