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 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; all these macros internally use format_args!.
To convert a single value to a string, use the to_string method. This
will use the Display formatting trait.
To concatenate literals into a &'static str, use the concat! macro.
§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"); // => "test"
format!("hello {}", "world!"); // => "hello world!"
format!("x = {}, y = {val}", 10, val = 30); // => "x = 10, y = 30"
let (x, y) = (1, 2);
format!("{x} + {y} = 3"); // => "1 + 2 = 3"Run