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

Brandon Knope bknope at me.com
Tue May 31 15:08:35 CDT 2016

```What is wrong with:

if let y = y && x < z

They are, after all, independent from each other.

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
> }
> ```
>
>
> ```
> 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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