> On May 2, 2016, at 1:08 PM, David Waite via swift-evolution
> <[email protected]> wrote:
>
>> The reason is simple: most developers don’t grok pattern matching.
>> Particularly for people new to swift, “if let” is taught as a magic for
>> dealing with optionals (which it is). This is a very useful mechanic when
>> working in Swift, and this way of thinking is fine. Optionals are very
>> prominent, and having special sugar for dealing with them is important, even
>> as people grow to become swift experts in time.
>>
>> Going with the proposal would definitely simplify the language ('if case’
>> could probably go away), but would force everyone, all the time, to think
>> about pattern matching. This would be a barrier to entry that many
>> programmers should never have to face. The fact that many people don’t
>> think about things in terms of pattern matching is the root cause for the
>> comments about “it seems weird that the question mark is on the LHS of the
>> assignment”.
>>
>> Finally, some may argue that making pattern matching more prominent would
>> help teach pattern matching and get more people to use it. That may be
>> true, but our goal here is to build a pragmatic language that helps people
>> get things done, not push to one specific language feature. I personally
>> love pattern matching (and was the one who drove and implemented the Swift 2
>> pattern matching enhancements), but it is an esoteric and special case
>> feature. It makes sense for it to be “buried” under “if case”: those who
>> are unfamiliar with the syntax have something they can google for.
>>
> My issue is that while one needs to have a special behavior in this case to
> combine conditional logic and variable assignment, the current shorthand is
> nonintuitive/inconsistent. The current syntax makes it look like you are
> saying “let y=x”, and that now assignment has different behaviors if you are
> inside or outside a conditional. Why does assignment sometime cast off
> optionality?
>
> let x:Optional = 1 // x: Int? = 1
>
> if let y = x {
> print(y.dynamicType) // Int
> }
> let y = x
> print(y.dynamicType) // Optional<Int>
>
> If there were a syntax like “if let y = some x”, then it would be clear that
> there is more to this statement than an assignment, it would make it clearer
> why you can’t cast off optionality on other assignments, as well as possibly
> being a segue to learning about full pattern matching.
>
> -DW
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This to me is the most bizarre thing about the if-let construct. Elsewhere in
the language ? indicates conditional unwrapping.
This would make more sense to me:
if let y = x? {
print(y.dynamicType) // Int
}
My issue with the proposed pattern matching syntax is that it looks like
assignment, which I think confuses people. This is one thing that the current
case syntax helps to mitigate.
if let y? = x {
print(y.dynamicType) // Int
}
Not that I’m suggesting this exactly, but the for-loop syntax works well. Maybe
there is a more clear pattern matching syntax?
if let y? in x {
print(y.dynamicType) // Int
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