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

[Brandon Knope]

What is wrong with:

if let x = x where x > 10, y != 5, let z = z where z != x

Just as a contrived example?

Brandon 

> On May 31, 2016, at 4:03 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
> 
>> On Tue, May 31, 2016 at 2:59 PM, Brandon Knope <bknope at me.com> wrote:
>> Except "b" is the main focus of the where clause and b was just in the preceding if condition. 
>> 
>> I feel like we are trying to find ways to break the current where clause even though we've enjoyed it for almost a year now. I had no idea it was problematic and restrictive. I thought it made its intent very clear...leading to very readable code. 
>> 
>> Pretty soon almost every construct but conditionals will be allowed to have where clauses, and THAT seems inconsistent to me. 
>> 
>> ...what exactly is the current problem? Can someone show me a real world example?? I've already forgotten it in all of this discussion -_-
> 
> The origin of the problem is a simple question: how does one test for something unrelated to the variable that's bound in an `if let` statement? The answer is: in today's Swift, any such test after the first `let` must come after `where`. This is problematic and restrictive because one is forced to imply a semantic relationship that doesn't exist.
>  
>> Brandon 
>> 
>>> On May 31, 2016, at 3:47 PM, Xiaodi Wu via swift-evolution <swift-evolution at swift.org> 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
>>> ``` 
>>> 
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> 
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