Macro alloc::format

macro_rules! format {
    ($($arg:tt)*) => { ... };
}

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 the formatting syntax documentation in std::fmt for details.

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.

Panics

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.

Examples

format!("test");
format!("hello {}", "world!");
format!("x = {}, y = {y}", 10, y = 30);
let (x, y) = (1, 2);
format!("{x} + {y} = 3");