11 ms·

Your specific example sounds like the kind of thing addressed by more powerful structure: labelled break, as appears in Java, JS, Rust and Swift (among others,

• nickpsecurity 9y ago
  It's why some of us built 4GL's, DSL's, preprocessors, and so on that added stuff to such languages but extracted to purely that language. Mine was a BASIC with macros translated to C w/ safety checks.
• userbinator 9y ago
  Unfortunately, in my experience the abuse of labelled breaks to avoid gotos tends to be even worse than abuse of regular breaks, since the label no longer shows immediately where the flow goes; it only labels the start of the block, when what you really want to see is the end.
  • dbaupp 9y ago
    I guess that could indeed be annoying for reading code, especially if the labelled block/loop is very long (I personally usually end up using these for short nested loops, longer loops usually get broken out into separate functions, and the biggest teams/programs I've worked on haven't been using languages that have this feature). That said, the extra structure/more restrictions of labelled breaks lends itself to compilers and other tooling being more helpful, both for optimisations (although SSA + basic blocks that most compilers now use makes this somewhat irrelevant) and for catching mistakes while, for instance, refactoring. In any case, I strongly disagree that labelled breaks aren't better than regular breaks: the chains of booleans required otherwise are very annoying and error prone.
• sedachv 9y ago
  Labelled break is strictly less powerful than gotos, and IMO its implementation in Java is far inferior to the block Common Lisp special form (https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node85.html https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node85.html) because s-expressions make the lexical scoping unambiguously visible. IMO there is no good substitute for gotos when writing transpilers (and certain interpreters) and low-level concurrency code. The Common Lisp prog macro is the best way that I have seen to use gotos (https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node91.html https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node91.html).
  • dbaupp 9y ago
    Of course it is strictly less powerful than gotos. That's actually the point of the more structured constructs: they are more restrictive and so can be reasoned about more easily. Note that I'm specifically piking up on labelled break/continue as a substitute for nested loops like the following while ... { bool shouldBreakOuter = false; while ... { ... shouldBreakOuter = true; break; } if (shouldBreakOuter) break; } since that what the original comments description sounded like. Being a rather general control flow mechanism, there are of course other uses of goto which this doesn't cover. That said, I'm not sure I understand the comparison: the lexical scoping doesn't seem to be ambiguous in Java. Could you expand on what you mean?
    • sedachv 9y ago
      If you visualize nested scopes as indent levels, the labelXYZ: sits in an indent level above where it is visible. Not only that, but labelXYZ: does not come before the statement that it transfers control to, but two statements before. If all that was not bad enough, most people format the labeled statement to sit at the same indentation level. The combination of these three things is pretty much the worst possible when it comes to reading code. Compare this to block/tagbody/prog and their indentation conventions in Common Lisp.