I was a bit surprised to find out (https://forum.dlang.org/post/csiwyetjkttlxxnwndif@forum.dlang.org) that compile time foreach-loops can be used inside switch-statements. I tried the following:

import std.stdio;
import std.typecons;

void foo(string s) {
    enum es = tuple("a", "b", "c");
    switch (s) {
      foreach (e; es) {
        case e:
            writeln("matched ", e);
            break;
      }
    default:
        writeln("no match");
        break;
    }
}

void main() {
    foo("a");
}

However, this prints both "matched a" and "no match". It seems like either the break or the default: label is ignored. In this example I could have used return of course, but is this behavior correct?

On Friday, 21 April 2017 at 19:09:25 UTC, Johan Fjeldtvedt wrote:
> void foo(string s) {
>     enum es = tuple("a", "b", "c");
>     switch (s) {
>       foreach (e; es) {
>         case e:
>             writeln("matched ", e);
>             break;
>       }

Let me remove some surrounding stuff and ask you what happens:

       foreach (e; es) {
         if(s == c) {
             writeln("matched ", e);
             break;
         }
       }


What does that break do?


Then realize that it does exactly the same thing when it is inside a switch... it always breaks the innermost thing, which happens to be this loop. (note that cases are not `breaked`, the switch is.)

On Fri, Apr 21, 2017 at 07:17:32PM +0000, Adam D. Ruppe via Digitalmars-d-learn wrote:
> On Friday, 21 April 2017 at 19:09:25 UTC, Johan Fjeldtvedt wrote:
> > void foo(string s) {
> >     enum es = tuple("a", "b", "c");
> >     switch (s) {
> >       foreach (e; es) {
> >         case e:
> >             writeln("matched ", e);
> >             break;
> >       }
> 
> Let me remove some surrounding stuff and ask you what happens:
> 
>        foreach (e; es) {
>          if(s == c) {
>              writeln("matched ", e);
>              break;
>          }
>        }
> 
> 
> What does that break do?
> 
> 
> Then realize that it does exactly the same thing when it is inside a switch... it always breaks the innermost thing, which happens to be this loop. (note that cases are not `breaked`, the switch is.)

Yeah, you want to label your switch statement, say `mySwitch:`, so that you can do a `break mySwitch;`


T

-- 
Knowledge is that area of ignorance that we arrange and classify. -- Ambrose Bierce

On Friday, 21 April 2017 at 19:17:32 UTC, Adam D. Ruppe wrote:
> On Friday, 21 April 2017 at 19:09:25 UTC, Johan Fjeldtvedt wrote:
>> void foo(string s) {
>>     enum es = tuple("a", "b", "c");
>>     switch (s) {
>>       foreach (e; es) {
>>         case e:
>>             writeln("matched ", e);
>>             break;
>>       }
>
> Let me remove some surrounding stuff and ask you what happens:
>
>        foreach (e; es) {
>          if(s == c) {
>              writeln("matched ", e);
>              break;
>          }
>        }
>
>
> What does that break do?
>
>
> Then realize that it does exactly the same thing when it is inside a switch... it always breaks the innermost thing, which happens to be this loop. (note that cases are not `breaked`, the switch is.)

*facepalm* Of course! Thanks.

On Friday, 21 April 2017 at 19:17:32 UTC, Adam D. Ruppe wrote:
> Then realize that it does exactly the same thing when it is inside a switch... it always breaks the innermost thing, which happens to be this loop. (note that cases are not `breaked`, the switch is.)

By coincidence I ran into this issue recently and assumed that break should break the switch too (and I hadn't read the boost::hana thread). Thanks for explaining, I thought it was probably a compiler bug and hadn't gotten round to investigating further.

So the compiler generates something like this:

	int s = 0;
	switch (s) {
		case 0:
			writeln("matched ");
		default:
			writeln("no match");
			break;
	}

If I compile the above I get:
Deprecation: switch case fallthrough - use 'goto default;' if intended

IMO the compiler should issue this warning with the OP's code.

On Saturday, 22 April 2017 at 11:56:31 UTC, Nick Treleaven wrote:
> If I compile the above I get:
> Deprecation: switch case fallthrough - use 'goto default;' if intended
>
> IMO the compiler should issue this warning with the OP's code.

https://issues.dlang.org/show_bug.cgi?id=7390#c4