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

Xiaodi Wu xiaodi.wu at gmail.com
Mon Jul 11 00:42:10 CDT 2016

Right. Both seem equally reasonable alternatives if a condition isn't
fulfilled where I'd like to continue pattern matching. Why do you say one
of these would be fair to disallow?
On Mon, Jul 11, 2016 at 00:39 Erica Sadun <erica at ericasadun.com> wrote:

> 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> wrote:
>> On Jul 10, 2016, at 10:34 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
>> On Sun, Jul 10, 2016 at 11:21 PM, Erica Sadun <erica at ericasadun.com>
>> wrote:
>>> On Jul 10, 2016, at 10:16 PM, Xiaodi Wu <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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