[swift-evolution] [Pitch] Add an all algorithm to Sequence

[Thorsten Seitz]

+1

> Am 03.04.2017 um 10:29 schrieb Daniel Duan via swift-evolution <swift-evolution at swift.org>:
> 
> I want to retract my nitpickings on argument labels; `all(equal:)` and `all(match:)` are the best names for these methods.
> 
> things all match condition?
> things all equal value?
> 
> If we accept `all` as a term of art (which I think we should), along with these labels the use site are very readable!
> 
>> On Mar 31, 2017, at 6:38 PM, Daniel Duan via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> nit: should these names be `all(matching)`/`all(equalTo)` per API Design Guidelines?
>>> On Mar 31, 2017, at 8:28 AM, Ben Cohen via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> Hi,
>>> 
>>> A short proposal for you as part of the algorithms theme. Hopefully non-controversial, aside from the naming of the method and arguments, about which controversy abounds. Online copy here: https://github.com/airspeedswift/swift-evolution/blob/9a778e904c9be8a3692edd19bb757b23c54aacbe/proposals/0162-all-algorithm.md
>>> 
>>> 
>>> Add an all algorithm to Sequence
>>> Proposal: SE-NNNN
>>> Authors: Ben Cohen
>>> Review Manager: TBD
>>> Status: Awaiting review
>>> Introduction
>>> 
>>> It is common to want to confirm that every element of a sequence equals a value, or matches a certain criteria. Many implementations of this can be found in use on github. This proposal adds such a method to Sequence.
>>> 
>>> Motivation
>>> 
>>> You can achieve this in Swift 3 with contains by negating both the criteria and the result:
>>> 
>>> // every element is 9
>>> !nums.contains { $0 != 9 }
>>> // every element is odd
>>> !nums.contains { !isOdd($0) }
>>> but these are a readability nightmare. Additionally, developers may not make the leap to realize contains can be used this way, so may hand-roll their own for loop, which could be buggy, or compose other inefficient alternatives:
>>> 
>>> // misses opportunity to bail early
>>> nums.reduce(true) { $0.0 && $0.1 == 9 }
>>> // the most straw-man travesty I could think of...
>>> Set(nums).count == 1 && Set(nums).first == 9
>>> Proposed solution
>>> 
>>> Introduce two algorithms on Sequence which test every element and return true if they match:
>>> 
>>> nums.all(equal: 9)
>>> nums.all(match: isOdd)
>>> Detailed design
>>> 
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