why not working ?

[violet snow]

fn main() {
    'mylabel:
        for i in 1..=10 {
            println!("{}", i)
            mylabel;
        }
}

[cloud wigeon]

What do you expect this to do?

[violet snow]

this is a loop label so i expect it to starting looping after i use the loop label name

[cloud wigeon]

Simply writing a loop label does nothing. (Also, you didn't write it correctly: labels should always be prefixed with a ')

They're meant to be used with break or continue

Also, you don't need one here: that loop will continue looping all on its own with no label at all.

[violet snow]

?play

fn main() {
    'mylabel:
        for i in 1..=10 {
            println!("{}", i);
            break 'mylabel;
        }
}

[dusky badger]

1```

[violet snow]

now it works

but what is the point ?

[cloud wigeon]

Nested loops

? eval

'label: loop {
  for i in 0..10 {
    println!("{i}");
    break 'label;
  }
}

[dusky badger]

0
()```

[violet snow]

i see

but

i have another question

why ' and : used both ? : alone can mean label so why is the apostrophe there ?

[cloud wigeon]

It can mean that in loops, but not when you use them

That's ambiguous in breaks

?eval

let x = 'label: loop {
  loop {
    let label = 10;
    break 'label label;
  }
};
x

[dusky badger]

10```

[cloud wigeon]

In loops, break can be given a value to break with. It can also be given a label. The ' disambiguates. And since labels have a ' there, they might as well have one everywhere

Not sure about why we have the :. That's probably to be more similar to what people expect from C-like languages?

[violet snow]

hmmmmmmm

i used goto in c

so having : there is not an issue

but

having both colon and apostrophe

a little confusing

[cloud wigeon]

Bright side is, labels are really rare

Break/continue in nested loops is very uncommon.

Even less common is their other use

let x = 'label: {
  break 'label 5;
}
x

You can break out of normal blocks, but only if they're labelled.

Basically a forward-only goto, though it avoids most if the issues of that statement by being tied to a scope

[rigid loom]

(which also use :)

[violet snow]

i see

there is a lot of ambiguity

[cloud wigeon]

In case it wasn't obvious, I agree having both is weird

😄

[violet snow]

hhh yeah

[rigid loom]

is there?

[violet snow]

not only this

but not an issue

?eval

fn main() {

    let mysentence : std::string::String = std::string::String::from("hello world");

    'start :

        for i in mysentence.chars() {
            if i == 'e' {
                std::println!("{}", i);
                break 'start;
            }
        }
}

[dusky badger]

e```

[violet snow]

thanks for the comments guys

[upper charm]

?play