[swift-evolution] For... else

[Félix Cloutier]

This is more a demonstration that the for...else construct isn't obvious than a solution to the problem. In Python, the else branch of a for loop is executed when you went through all the iterations without breaking ("when the loop condition becomes false", which doesn't happen if you break from the loop).

Félix

> Le 25 janv. 2016 à 23:14:23, Andrew Bennett via swift-evolution <swift-evolution at swift.org> a écrit :
> 
> This may do what you want:
> 
>     let values: [Int] = [1,2,3,4]
>     if let sequence = nonEmptySequence(values) {
>         for element in sequence {
>             print("element: \(element)")
>         }
>     }
>     else {
>         print("empty!")
>     }
> 
> It's also more flexible, you can do work after the for loop (that work won't execute in the else), you can also use PeekSequence directly to get the first value. This is handy for something like an average (reduce) where you don't necessarily have a zero value.
> 
> The implementation can be found here: https://github.com/therealbnut/PeekSequence <https://github.com/therealbnut/PeekSequence>
> 
> 
> On Tue, Jan 26, 2016 at 12:59 AM, Matthew Johnson via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> 
> 
> Sent from my iPad
> 
> On Jan 25, 2016, at 3:41 AM, Howard Lovatt via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> 
>> It would be easy enough to add:
>> 
>> func forEach(
>>     @noescape elements body: (Element) throws -> Void,
>>     @noescape otherwise otherwise: () throws -> Void
>> ) rethrows
>> 
>> to the standard library or write it yourself.
> 
> Not unless / until we get the ability for a noescape closure to influence control flow (break, return, etc).  Even then this is clunkier than adding else to the language would be.
> 
>> 
>> On 23 Jan 2016, at 12:59 PM, Félix Cloutier via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>>> I frequently need something like that and I'd like to have it in Swift too.
>>> 
>>> Félix
>>> 
>>>> Le 22 janv. 2016 à 13:22:45, Ben Langmuir via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> a écrit :
>>>> 
>>>> Previous discussion here:
>>>> https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151207/001110.html <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151207/001110.html>
>>>> 
>>>> 
>>>>> On Jan 22, 2016, at 8:22 AM, Lee M via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>> 
>>>>> This has likely been discussed already, but I haven't been able to find it anywhere.
>>>>> Example:
>>>>> 
>>>>>    let items: Int = []
>>>>> 
>>>>>    for item in items {
>>>>>        print(item)
>>>>>    }
>>>>>    else {
>>>>>        print("No items")
>>>>>    }
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>>>> 
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