Why can't format! be used in the procedure macro?

help
1

Why can't format! be used in the procedure macro?

already use std::fmt;

2

It's best to use globally qualified paths in your macro for all type references. This will avoid ambiguities caused by name collisions with other types in the namespace where the macro is expanded.

format! exists at ::std::format!, not ::std::fmt::format!:

macro_rules! hello {
    ($x:expr) => {
        ::std::format!("Hello, world! {}", $x)
    }
}

fn main() {
    println!("{}", hello!(123 + 456));
}