Macro concat 

macro_rules! concat {
    ($($e:expr),* $(,)?) => { ... };
}

Concatenates literals into a static string slice.

This macro takes any number of comma-separated literals, yielding an expression of type &'static str which represents all of the literals concatenated left-to-right.

Integer and floating point literals are stringified in order to be concatenated.

Examples

let s = concat!("test", 10, 'b', true);
assert_eq!(s, "test10btrue");