[swift-evolution] for in? optionalCollection {

[André “Zephyz” Videla]

Ah I see you point a bit better.

But I don't agree with your example, since it can be easily expressed with

test?.prefix(while: { $0 != 42}).forEach { i in
    print(i)
}

But arguing about examples is besides the point, I would like to stop here.

I have a question for you. How do you think we could use this pattern in the generalised situation:

if condiition {
    for thing in condition {
    }
}

for example

enum Result<T> {
    case success(T)
    case failure(Error)
}

let result: Result<[Int]> = .success([0,1,2,3])

if case .success(let arr) = result {
    for e in arr {
        print(e)
    }
}

Maybe it would be nice to write something along the lines of

for e in case .success(let arr) = result {
    
}

or even
for e in arr where .success(let arr) = result {
    
}

therefore the "in?" syntax would be sugar for
for i in array where let array? = test {
    
}

> On 11 Feb 2017, at 13:22, Tino Heth <2th at gmx.de> wrote:
> 
>> I don't think this use case warrants a syntax change since it can already be expressed quite elegantly with
>> 
>> let test: [Int]? = nil
>> 
>> test?.forEach { i in
>>     print(i)
>> }
> 
>> What about just use
>> 
>> test?.forEach { print($0) }
> 
> This works for the simple example, but it isn't as powerful:
> 
> if let test = test {
> 	for i in test {
> 		if i == 42 {
> 			break
> 		}
> 	}
> }
> 
> You could add
> func forEach(_ body: (Element) throws -> Bool) rethrows 
> 
> but even this would be less powerful as a loop, which allows you to break, continue or return as you like.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20170211/44859752/attachment.html>