[swift-evolution] [swift-evolution-announce] [Review] SE-0099: Restructuring Condition Clauses

[Xiaodi Wu]

On Tue, May 31, 2016 at 3:43 PM, Brandon Knope <bknope at me.com> wrote:

> Why would that argue for the removal of where
>
> if let y = y where y != 5 && x < z
>
> I would still prefer:
> if let y = y where y != 5, x < z, let z = someOptional where z == 10
>
> To me, where still has a place. And that place is saying "hey this is a
> recently introduced or shadowed variable, so don't go looking very far for
> what is referring to".
>
> If I understand correctly, this would be rewritten in the proposed syntax
> as:
>
> if let y = y; y != 5; x < z; let z = someOptional; z == 10 { }
>
> Which technically could be written as:
>
> if let y = y; x < z; let z = someOptional; z == 10; y != 5 { } // y != 5
> arbitrarily moved to the end
>
> Now y != 5 is at the end and a quick glimpse of this line could be
> confusing:
> 1. Is this y a previous variable like x is?
> 2. Is it a shadowed variable?
>


Sure; but as has been mentioned on this list before, these concerns about
style are what linters are for, not the compiler.


>
> This kind of information is lost while glancing the line (and people do
> glance especially with long conditional clauses). This makes having where
> relevant in my opinion. It aids in readability and expressiveness.
>
> Brandon
>
>
> On May 31, 2016, at 4:25 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
>
> On Tue, May 31, 2016 at 3:16 PM, Brandon Knope <bknope at me.com> wrote:
>
>> And why couldn't we propose that it should?
>>
>
> And that is this proposal; the options considered for the spelling are
> comma, semicolon, and `&&`.
>
> Now we circle back to my earlier point. The introduction of any of these
> would argue for the elimination of `where`, for the reasons I've stated
> above. Briefly, everything that can be expressed using `where` could be
> expressed using the comma, semicolon, or `&&`. Since there is no good way
> to enforce the semantic relationship requirement for `where`, only a proxy
> rule about variable names can be contemplated, which as I've demonstrated
> is ineffective.
>
> If you're asking why commas or semicolons have been proposed instead of
> `&&`, that argument has been made above by others.
>
>
> Brandon
>>
>> On May 31, 2016, at 4:14 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
>>
>> On Tue, May 31, 2016 at 3:08 PM, Brandon Knope <bknope at me.com> wrote:
>>
>>> What is wrong with:
>>>
>>> if let y = y && x < z
>>>
>>> They are, after all, independent from each other.
>>>
>>
>> That won't compile.
>>
>>
>> Brandon
>>>
>>> On May 31, 2016, at 3:59 PM, Xiaodi Wu via swift-evolution <
>>> swift-evolution at swift.org> wrote:
>>>
>>> On Tue, May 31, 2016 at 2:51 PM, Christopher Kornher via swift-evolution
>>> <swift-evolution at swift.org> wrote:
>>>
>>>>
>>>> On May 31, 2016, at 1:47 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
>>>>
>>>>
>>>>
>>>> On Tue, May 31, 2016 at 2:45 PM, Christopher Kornher via
>>>> swift-evolution <swift-evolution at swift.org> wrote:
>>>>
>>>>>
>>>>>> Not allowed:
>>>>>> …
>>>>>> let a = a
>>>>>> let b = b where b > 10 && a > 5
>>>>>>
>>>>>
>>>>> Why would this not be allowed by your rule? You're making use of `b`
>>>>> in your where clause. As I demonstrated above, essentially any assertion
>>>>> can be rewritten to work around your rule. In general:
>>>>>
>>>>>
>>>>> It is not allowed because  ‘a’ is defined in the line above. It must
>>>>> be defined in the ‘if let’ associated with the where in which it is
>>>>> mentioned.
>>>>>
>>>>
>>>> That's a much more restrictive where clause than you proposed earlier.
>>>> You'd not be able to write:
>>>>
>>>> ```
>>>> let b = b where b > anyOtherVariable
>>>> ```
>>>>
>>>>
>>>> The definition is not a formal one, but that was the intent.
>>>>
>>>> ```
>>>> let b = b where b > anyOtherVariable
>>>> ```
>>>>
>>>> is legal as long as `anyOtherVariable` is not defined within the entire
>>>> condition clause
>>>>
>>>
>>>
>>> You can propose that rule, but it doesn't solve the issue. If, today,
>>> I've got
>>>
>>> ```
>>> let x = 1
>>> let y: Int? = 2
>>> let z = 3
>>>
>>> if let y = y where x < z {
>>>   // do stuff
>>> }
>>> ```
>>>
>>> your rule simply forces
>>>
>>> ```
>>> if let y = y where y == y && x < z {
>>>   // do stuff
>>> }
>>> ```
>>>
>>> The point is, the semantic relationship between what comes before and
>>> after `where` exists in the mind of the human reader only.
>>>
>>> _______________________________________________
>>> swift-evolution mailing list
>>> swift-evolution at swift.org
>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>
>>>
>>
>
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