CODEWITHSUNDEEP
stringconcatenationrust
elleciel
elleciel

Reputation: 2567

What is the most idiomatic way to concatenate integer variables?

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()
}

Upvotes: 7

Views: 3575

Answers (2)

Shepmaster
Shepmaster

Reputation: 431449

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

Upvotes: 4

Dogbert
Dogbert

Reputation: 222268

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)
}

Upvotes: 13

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