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.
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");Run