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Comment by atq2119 | Hacker News Reader

Not mentioned in the article but kinda neat: you can label such a block and break out of it, too! The break takes an argument that becomes the value of the block that is broken out of.

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I just learned this one, and am gradually starting to use it! It applies for loops too. I saw it in ChatGPT code, and had to stop and look it up. Rust is a big language, for worse and for better.

I wouldn't call Rust "a big language" because of labeled break. This is a pretty standard language feature, you can do the same in C (and therefore C++), Go, Javascript, Java, C#...

Those languages don't treat blocks as expressions, so you really can't do the same thing there. Something very similar, yes. But not the same.

Those languages aren't expression-oriented, so you would need to assign the result to a previously-initialized variable in a higher scope. But that just makes this pattern clunkier in those languages. This subthread is about jumping to labels, which is a relatively obscure yet widespread feature supported by many languages (though C and Go allow forward jumps, and the rest only allow backward jumps, since the latter ensures that control flow does not become irreducible).

  break 'label value;

... is something to be used very sparingly. I reckon I write a new one about once a year.

Very often if you think harder you realise you didn't want this, you should write say, a function (from which you can return) or actually you didn't want to break early at all. Not always, but often. If you write more "break 'label value" than just break then you are almost certainly Doing It Wrong™.

Not having put it into practice yet, there is a pattern I use regularly which I plan to replace with the labeled one: I set a flag at the top of the loop I have an inner loop. The inner loop can set this flag. Directly past the inner loop, I check for the flag, then break. I am pretty sure this is exactly what the labeled break is for.

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