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

[Xiaodi Wu]

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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