DIP 1010--Static foreach--Formal Review

[Steven Schveighoffer via Digitalmars-d]

On 7/10/17 4:53 AM, Mike Parker wrote:
> As promised, since there has been zero feedback on DIP 1010, "Static 
> foreach", in either the Draft or Preliminary review rounds, I'm going to 
> skip the normal two-week feedback cycle on the Formal review. If there 
> are no major criticisms or objections raised in this thread, then 
> sometime on Thursday of this week I'll send Walter & Andrei an email 
> kicking off the decision process.
> 
> So, if you have any thoughts on the DIP, now is the time to express them.
> 
> Thanks!
> 
> https://github.com/dlang/DIPs/blob/master/DIPs/DIP1010.md
> 

A few things:

1. I can't wait for this to get in. I'm anticipating success :)

2. I see no point in having foreach(enum i; 0.. 3) when static 
foreach(i; 0 .. 3) works just fine?

3. The only controversial part I see is that `break` doesn't break from 
the foreach loop. While I agree with the reasoning, and support that 
concept, the truth is we currently have a "poor man's" static foreach 
using a foreach over a tuple, and that DOES break from the loop.

For instance:

size_t idx;
switch(someval)
{
    case something:
       foreach(v; AliasSeq!(1, 2, 3))
       {
           if(shouldBreak(v))
               break; // today, this jumps to moreProcessing() line
       }
       moreProcessing();
       break;
}

If I replaced foreach with static foreach(v; 1 .. 4), it now breaks out 
of the switch?

As much as I would rather see the proposed behavior, I feel it's too 
confusing given the existing foreach behavior. I think in this case, you 
have to require a break label.

A possible deprecation path:

1. In the case where "static foreach" is inside another construct that 
allows breaking, require a break label. However, foreach over a tuple 
would continue to exhibit today's behavior.
2. print warning message for foreach over a tuple that contains a break 
without a label. Warn users that a future version will not allow 
breaking from the foreach.
3. disallow breaking out of the foreach directly (i.e. jumping to the 
closing brace of the loop), even if there is a label (you can surround 
foreach with a do{} while(false) if you need this behavior).
4. Remove the requirement for labeling. Both static foreach and foreach 
on a tuple do not break from the loop construct.

-Steve