Levi et al,
On Fri, Sep 18, 2015 at 10:11 AM, Levi Morrison <le...@php.net> wrote:
> On Thu, Sep 17, 2015 at 5:52 PM, John Bafford <jbaff...@zort.net> wrote:
>> On Sep 17, 2015, at 19:16, Bob Weinand <bobw...@hotmail.com> wrote:
>>>
>>>> Am 18.09.2015 um 01:06 schrieb Rowan Collins <rowan.coll...@gmail.com>:
>>>>
>>>> This has come up in passing a few times recently, but I'm not sure there's
>>>> ever been a dedicated discussion of it: would it be useful for PHP to have
>>>> a built-in Enumeration type, and if so, how should it look?
>>>
>>> I like enums in general, but I'd like to note that there's already a RFC in
>>> draft by Levi:
>>>
>>> https://wiki.php.net/rfc/enum <https://wiki.php.net/rfc/enum>
>>>
>>> As far as I know, the RFC is already fairly final and just lacks an
>>> implementation.
>>>
>>> So, I'd consider bikeshedding an actual RFC first.
>>
>>
>> If we’re bikeshedding, one feature I would really like to see, with
>> typehinting, is warnings if all cases of an enum aren’t handled in a switch.
>> So, for example, given our example Weekdays enum, if I wrote this code:
>>
>> switch(Weekday $someWeekday) {
>> case Weekday::MONDAY: break;
>> case Weekday::TUESDAY: break;
>> }
>>
>> By providing the typehint, I’m indicating that I want to get a warning/error
>> that the switch does not cover all enum values. This would be very handy if
>> an enum value is added after initial development and someone misses a switch
>> statement in cleanup.
>>
>> The typehint would also allow generating a warning if someone did something
>> like
>>
>> switch(Weekday $someWeekday) {
>> //case … all the weekdays: break;
>> case ‘I am not a Weekday’: echo ‘Generate a fatal error here because
>> string is not a Weekday.’;
>> }
>
> I've looked into this but not in the same syntax you've provided. I
> was exploring a `match` construct that has different semantics:
>
> match ($foo) {
> case Weekday::Monday: {
> echo "Monday";
> } // it is not possible to fall-through with match/case
>
> case Weekday::Tuesday: echo Monday; // single expression
> doesn't need braces
> } // if it hits the end without a match a runtime error will be emitted
>
> I think this fits into the dynamic behavior of PHP a little better
> than forcing a case for each enum value at compile-time, even if it
> was possible (I suspect it is not).
This is basically pattern matching. And while I'd LOVE to see support
for it in PHP, I think it's a bit off-topic here. Perhaps a new thread
could be opened for it (or ideally a RFC)...?
As far as enums, I wonder if they would be necessary if we supported
algebraic types, since you could define an "enum" as a virtual type:
const MONDAY = 0;
const TUESDAY = 1;
const WEDNESDAY = 2;
const THURSDAY = 3;
const FRIDAY = 4;
use MONDAY | TUESDAY | WEDNESDAY | THURSDAY | FRIDAY as WEEKDAY;
function foo(WEEKDAY $day) {
// must be an integer 0-4, or castable to 0-4 unless strict_types is on.
}
Just a thought...
Anthony
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