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

[Xiaodi Wu]

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.
>
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