[swift-evolution] [Pitch] Introduce continue to switch statements

Erica Sadun erica at ericasadun.com
Mon Jul 11 00:39:23 CDT 2016

Because one says "consider the next case" and the other says "do not consider the next case"

> On Jul 10, 2016, at 11:03 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
> I know how it works. Why would you say that it's reasonable to prohibit fallthrough when continue is used? The difference between it and break is that Swift chooses the latter to be implied, and obviously we cannot prohibit break.
> On Sun, Jul 10, 2016 at 23:51 Erica Sadun <erica at ericasadun.com <mailto:erica at ericasadun.com>> wrote:
>> On Jul 10, 2016, at 10:34 PM, Xiaodi Wu <xiaodi.wu at gmail.com <mailto:xiaodi.wu at gmail.com>> wrote:
>> On Sun, Jul 10, 2016 at 11:21 PM, Erica Sadun <erica at ericasadun.com <mailto:erica at ericasadun.com>> wrote:
>>> On Jul 10, 2016, at 10:16 PM, Xiaodi Wu <xiaodi.wu at gmail.com <mailto:xiaodi.wu at gmail.com>> wrote:
>>> Given patterns A, B, C, and D, suppose a value x matches A, C, and D, whereas another value y matches B and D, and a third value matches B and C. When evaluating x, y, or z, which statements are executed in the following switch statement? How many of these reach the default case? What happens if I append `fallthrough` at the end of case D? What happens if I move case B after case D? (Yes, I know it is possible to figure it out [my understanding of the answer to the first question is appended below], but I hope you'll agree with me that this is much more difficult to decipher than any switch statement that's currently possible.)
>>> ```
>>> switch x /* or y, or z */ {
>>> case A:
>>>   // ...
>>>   continue
>>> case B:
>>>   // ...
>>>   if C ~= x /* or y, or z, whichever is switched over */ {
>>>     continue
>>>   }
>>>   fallthrough
>> I'd say it would be fair to disallow continue and fallthrough to occur in the same clause
>> Why should `fallthrough` be prohibited but implicit `break` become mandatory in such a clause? If `continue` were to be implemented in this context, I'd want the full power of the keyword, including being allowed to `continue` conditionally, `continue` with different labels, and round out the case if no conditions are satisfied with either `fallthrough` or `break` (or, for that matter, `return`, etc.).
> I do not understand. `break` is already implicit unless no other code is used. 
> case something:
>    if condition { continue }
>    // ends here. the compiler knows not to go forward and it's not an empty clause
> case somethingElse:
> `fallthrough` means "ignore the next case statement and execute its clause".
> -- E

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