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

[Xiaodi Wu]

On Fri, Mar 31, 2017 at 12:14 PM, Joshua Alvarado via swift-evolution <
swift-evolution at swift.org> wrote:

> Nice addition!
>
> What do you think of equal parameter named to are?
>
> nums.all(equal: 9)
>
> nums.all(are: 9)
>
>
> I think it reads better and adds an explicit action of what is being
> checked.
>
>
>> if nums.all(are: 9) { print("all elements are 9") }
>
>
By the same token, `all(match:)` could be renamed `all(are:)`, and therein
lies the problem.
I like `equal`. It explains what operation is being performed to determine
if two things "are" the same and distinguishes the function from `match`.

On Fri, Mar 31, 2017 at 9:28 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/airsp
>> eedswift/swift-evolution/blob/9a778e904c9be8a3692edd19bb757b
>> 23c54aacbe/proposals/0162-all-algorithm.md
>>
>>
>> Add an all algorithm to Sequence
>>
>>    - Proposal: SE-NNNN
>>    - Authors: Ben Cohen <https://github.com/airspeedswift>
>>    - 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
>>
>> Add the following extensions to Sequence:
>>
>> extension Sequence {
>>   /// Returns a Boolean value indicating whether every element of the sequence
>>   /// satisfies the given predicate.
>>   func all(match criteria: (Iterator.Element) throws -> Bool) rethrows -> Bool
>> }
>> extension Sequence where Iterator.Element: Equatable {
>>   /// Returns a Boolean value indicating whether every element of the sequence
>>   /// equals the given element.
>>   func all(equal element: Iterator.Element) -> Bool
>> }
>>
>> Source compatibility
>>
>> This change is purely additive so has no source compatibility
>> consequences.
>> Effect on ABI stability
>>
>> This change is purely additive so has no ABI stability consequences.
>> Effect on API resilience
>>
>> This change is purely additive so has no API resilience consequences.
>> Alternatives considered
>> Not adding it.
>>
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>>
>>
>
>
> --
> Joshua Alvarado
> alvaradojoshua0 at gmail.com
>
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>
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