> On Jan 11, 2017, at 01:29, David Sweeris via swift-evolution
> <swift-evolution@swift.org> wrote:
>
>
>> On Jan 11, 2017, at 01:11, Freak Show <freaksho...@mac.com> wrote:
>>
>>
>>> On Jan 7, 2017, at 23:37, Derrick Ho <wh1pch...@gmail.com> wrote:
>>>
>>> I think pattern matching is the most compelling reason to keep tuples.
>>>
>>> If they were gone, how would we replace the following?
>>>
>>> switch (a, b) {
>>> case (value1, value2):
>>> case (value3, value4):
>>> }
>>
>> I meant to mention this: Smalltalk - Objective C's mother language - has no
>> switch statement (or 'if' or loops either). The language is incredibly
>> malleable because it only does one thing - send messages to objects and all
>> the language constructs are in the library. It would take very little time
>> to add one. Off and on someone does it as an exercise but it never sticks.
>>
>> Instead, you just use a dictionary of closures. An Objective C equivalent
>> might be:
>>
>> NSDictionary* switch = @{
>> @[@0,@1]: ^{ NSLog(@"zero one"); },
>> @[@1,@1]: ^{ NSLog(@"one one"); }
>> };
>>
>> NSArray* pair = @[@3, @5];
>>
>> (switch at:pair ifAbsent:^{})(); //where at:ifAbsent: is added in the
>> Smalltalk style as an extension.
>>
>> The Smalltalk equivalent (much less ugly because of the lack of @'s) is
>>
>> switch := {
>> #(0 1) -> [ Transcript nextPutAll: 'zero one' ] .
>> #(1 1) -> [ Transcript nextPutAll: 'one one' ] .
>> #(1 2) -> [ Transcript nextPutAll: 'one two' ] .
>> } asDictionary.
>>
>> (switch at: pair ifAbsent:[ [] ]) value.
>>
>> So its not like this is some kind of key feature. Switch's vs dictionaries
>> of closures - pretty much the same thing as pattern matching goes. The only
>> thing you have to do is put an object at key that identifies itself as equal
>> to the pattern you will throw at it.
>
> I suspect that's a fair bit slower than a switch statement. I'm not in front
> of my computer, so I can't prove it, though.
Also, Swift's dictionary requires its keys to conform to `Hashable`, which
would mean we'd have to create a formal struct *and* the "==" method for it
would have to act as a pattern matched instead of checking equality. I suspect
this could break a great many things that depend on "Equatable" meaning what it
says.
- Dave Sweeris (again)
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