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

[Xiaodi Wu]

On Tue, May 31, 2016 at 3:16 PM, Brandon Knope <bknope at me.com> wrote:

> And why couldn't we propose that it should?
>

And that is this proposal; the options considered for the spelling are
comma, semicolon, and `&&`.

Now we circle back to my earlier point. The introduction of any of these
would argue for the elimination of `where`, for the reasons I've stated
above. Briefly, everything that can be expressed using `where` could be
expressed using the comma, semicolon, or `&&`. Since there is no good way
to enforce the semantic relationship requirement for `where`, only a proxy
rule about variable names can be contemplated, which as I've demonstrated
is ineffective.

If you're asking why commas or semicolons have been proposed instead of
`&&`, that argument has been made above by others.


Brandon
>
> On May 31, 2016, at 4:14 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
>
> 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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>>
>>
>
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