How to create a string slice from arithmetic in one line?

Asked Nov 20 '19 at 07:02

Active Nov 20 '19 at 12:07

Viewed 81 times

In rust, how to create a string slice &str, from a arithmetic expression, say 1 * 2 * 3, in one line?

i.e. the following code:

fn main() {
    let a = vec!["x", &(1 * 2 * 3).to_string()];
    println!("{:?}", a)
}

Playground

produces the following error:

error[E0716]: temporary value dropped while borrowed
 --> src/main.rs:4:24
  |
4 |     let a = vec!["x", &(1 * 2 * 3).to_string()];
  |                        ^^^^^^^^^^^^^^^^^^^^^^^ - temporary value is freed at the end of this statement
  |                        |
  |                        creates a temporary which is freed while still in use
5 |     println!("{:?}", &a);
  |                      -- borrow later used here
  |
  = note: consider using a `let` binding to create a longer lived value

But doing as the compiler suggests would require an extra statement:

let num = (1 * 2 * 3).to_string();
let a = vec!["x", &num];

Is there a way to get rid of the let num = … statement?

edited Nov 20 '19 at 12:07

Stargateur

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asked Nov 20 '19 at 07:02

Incömplete

@Jmb now it doesn't ... – Incömplete Nov 20 '19 at 08:40
Do you want a string representation of the expression value, or the expression itself? (1 * 2 * 3) should be `"1 * 2 * 3"` or `"6"`? – Yuri Kovalenko Nov 20 '19 at 08:46
@YuriKovalenko `"6"` – Incömplete Nov 20 '19 at 08:57
You can't without a proc macro for example. You need at least a temporary variable which you can store the `String` in. The other solution would be to convert "x" into a string, by using `to_string` on it. – hellow Nov 20 '19 at 09:25
1

Is there a specific motivation for wanting to do this in one line? Knowing that might allow people to provide alternative approaches. – loganfsmyth Nov 20 '19 at 11:27
Also, is there a specific reason you need it as a string-slice? Using `String` instead would make it work in one line by converting the `"x"` to a `String` – Dragonseel Nov 20 '19 at 11:32
sometime compiler can but not this time. – Stargateur Nov 20 '19 at 12:06

How to create a string slice from arithmetic in one line?

0 Answers0