[swift-evolution] Proposal: Add function SequenceType.find()

[James Campbell]

But overloading the first method with a closure is a clever ide s

Sent from my iPhone

> On 30 Dec 2015, at 15:33, Donnacha Oisín Kidney <oisin.kidney at gmail.com> wrote:
> 
> +1 on this.
> 
> I see a lot of code like this:
> 
> sequence.filter(predicate).first
> 
> Which is of course is inefficient. However, the go-to optimisation:
> 
> sequence.lazy.filter(predicate).first
> 
> Is not necessarily better, and has some strange behaviour:
> 
> let array = [1, 2, 3, 4, 5, 6]
> func noisyPredicate(n: Int) -> Bool {
>   print(n, terminator: " ")
>   return n > 2
> }
> 
> array.lazy.filter(noisyPredicate).first
> // 1 2 3 1 2 3
> 
> AnySequence(array).lazy.filter(noisyPredicate).first
> // 1 2 3 4 5 6
> 
> If it’s called on a collection, the collection is only evaluated up until the element being looked for, but it’s done twice. If it’s called on a sequence, the whole sequence is evaluated, regardless of where the element is found.
> 
> I think that find is maybe not the best name, though. It’s not immediately clear that it doesn’t return an index. I’d prefer to call it first, as in:
> 
> extension SequenceType {
>   /// Returns the first element where `predicate` returns `true`, or `nil`
>   /// if such value is not found.
>   public func first(@noescape thatSatisfies: (Self.Generator.Element) throws -> Bool) rethrows -> Self.Generator.Element? {
>     for elt in self {
>       if try thatSatisfies(elt) {
>         return elt
>       }
>     }
>     return nil
>   }
> }
> 
> [1, 2, 3, 4, 5].first(thatSatisfies: (Int) throws -> Bool)
> 
> [1, 2, 3, 4, 5].first { $0 > 3 }
> 
>> On 30 Dec 2015, at 10:13, James Campbell via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> We should add the full collection of ruby methods http://matthewcarriere.com/06/23/using-select-reject-collect-inject-and-detect/
>> 
>> 
>> 
>> Sent from my iPhone
>> 
>>> On 30 Dec 2015, at 02:40, Keith Smiley via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> +1. We've added an extension for this and find it very useful.
>>>> On Tue, Dec 29, 2015 at 18:38 Kevin Ballard via swift-evolution <swift-evolution at swift.org> wrote:
>>>> I'm proposing a new extension method on SequenceType called find(). It's similar to CollectionType.indexOf() except it returns the element:
>>>>  
>>>> extension SequenceType {
>>>>     /// Returns the first element where `predicate` returns `true`, or `nil`
>>>>     /// if such value is not found.
>>>>     public func find(@noescape predicate: (Self.Generator.Element) throws -> Bool) rethrows -> Self.Generator.Element? {
>>>>         for elt in self {
>>>>             if try predicate(elt) {
>>>>                 return elt
>>>>             }
>>>>         }
>>>>         return nil
>>>>     }
>>>> }
>>>>  
>>>> -Kevin Ballard
>>>>  
>>>> 
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