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

[Brandon Knope]

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
> }
> ```
> 
> 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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