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Subject: Re: [std-proposals] Labeled 'continue' and 'break'
From: connor horman (chorman64_at_[hidden])
Date: 2020-03-10 19:50:16


I’m pretty sure Java has something similar, though that would have less
confusion (as you cannot use goto in Java). I would support the feature in
some way though, I find it rather annoying in some cases when I need to
exit nested loops.

On Tue, Mar 10, 2020 at 20:35 Jake Arkinstall via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> I think the break label syntax is a little bit confusing to the casual
> reader, given that it's actually going to jump past the loop described by
> the label. Continue too, to some extent, because it jumps to the evaluation
> of the condition, whereas the immediate code after the label is the
> initialisation.
>
> Of course, this confusion is just caused by expecting goto like behaviour,
> when the implementation would actually be a goto to a label *based* on
> the loop label*. I have actually seen goto used for this circumstance in
> relatively modern C++ code, particularly when the "return from a lambda"
> approach doesn't suffice (I.e. when you want to break from a number of
> loops that depend on a condition).
>
> I'd actually make the labels optional and have break N, where N is how
> many loops to break out of. Same goes for continue. I think this is neater,
> but that's probably some (rare) nostalgia from my PHP days.
>
> * such that
>
> label1: for(int i = 0; x < 5; x++){
> if(x % 3 == 1){
> continue label1;
> }else if(x % 3 == 2){
> break label1;
> }
> }
>
> would be equivalent to
>
>
> {
> int x = 0;
> while(x < 5){
> if(x % 3 == 1){
> goto label1_continue;
> }else if(x % 3 == 2){
> goto label1_break;
> }
> label1_continue:
> x++;
> }
> label1_break:
> }
>
>
> On Wed, 11 Mar 2020, 00:12 Ryan Nicholl via Std-Proposals, <
> std-proposals_at_[hidden]> wrote:
>
>>
>> I'd like to suggest adopting labeled break and continue statements,
>>
>> e.g.
>>
>> label1: for( int x = 0; x < 5; x++)
>> {
>> label2: for (int y = 0; y < 5; y++)
>> {
>> for (int z = 0; z < 5; z++)
>> {
>> std::cout << x << ',' << y << ',' << z << std::endl;
>> if (z+y == 8) continue label2;
>> if (z+x == 3) break label2;
>> if (x + y + z == 13) break label1;
>> }
>> }
>> }
>>
>> Other languages have it, and it's convenient with nested loops.
>>
>> --
>> Std-Proposals mailing list
>> Std-Proposals_at_[hidden]
>> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals
>>
> --
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> Std-Proposals_at_[hidden]
> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals
>



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