On: Format Strings in Rust 1.58

[georgyo]

At this point I should research it myself, but I'm on mobile currently.

But how would you print {x} in 1.57? I doubt you would escape it with {{ in that release. Maybe \{ then? Does that still work in 1.58?

This still smells fishy to me, but I need to dig deeper.

[jeroenhd → georgyo]

In previous Rust versions, you can't print {0} by printing `{x}`. Adding braces around variables turns them into named variables. For example:

    pub fn main() {
        let y = 4;
        println!("{x}", x=y);
    }

To print '{x}', you need to write:

    pub fn main() {
        let x = 4; // unused
        println!("{{x}}");
    }

[estebank → jeroenhd]

The last bit of information that GP might be missing is that

    pub fn main() {
        let x = 4; // unused
        println!("{x}");
    }

would previously be a compile time error (because the format! family of macros perform string interpolation at compile time):

    error: there is no argument named `x`
     --> <source>:3:15
      |
    3 |     println!("{x}");
      |               ^^^

So no new existing code will stop compiling, some things that were previously compile errors will now work.

[sodality2 → georgyo]

> I doubt you would escape it with {{ in that release

You would. Brackets were still escaping in that release because you would of course still do `println!("{}", x);`

[lmkg → georgyo]

You might be missing the fact that this applies only to format strings, not strings in general. The interpolation into curly brackets is done by the format! (or println!) macros, not a language feature of strings in general.