What is the most idiomatic way to concatenate integer variables?

问题

The compiler doesn't seem to infer that the integer variables are passed as string literals into the concat! macro, so I found the stringify! macro that converts these integer variables into string literals, but this looks ugly:

fn date(year: u8, month: u8, day: u8) -> String
{
    concat!(stringify!(month), "/",
            stringify!(day), "/",
            stringify!(year)).to_string()
}

回答1:

concat! takes literals and produces a &'static str at compile time. You should use format! for this:

fn date(year: u8, month: u8, day: u8) -> String {
    format!("{}/{}/{}", month, day, year)
}

回答2:

Also note that your example does not do what you want! When you compile it, you get these warnings:

<anon>:1:9: 1:13 warning: unused variable: `year`, #[warn(unused_variables)] on by default
<anon>:1 fn date(year: u8, month: u8, day: u8) -> String
                 ^~~~
<anon>:1:19: 1:24 warning: unused variable: `month`, #[warn(unused_variables)] on by default
<anon>:1 fn date(year: u8, month: u8, day: u8) -> String
                           ^~~~~
<anon>:1:30: 1:33 warning: unused variable: `day`, #[warn(unused_variables)] on by default
<anon>:1 fn date(year: u8, month: u8, day: u8) -> String
                                      ^~~

Note that all the variables are unused! The output of calling the function will always be the string:

month/day/year

来源：https://stackoverflow.com/questions/27965471/what-is-the-most-idiomatic-way-to-concatenate-integer-variables