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

[Brandon Trussell]

I like onlyContains() and containsOnly() so far.

On Mon, Apr 3, 2017 at 1:29 AM, Daniel Duan via swift-evolution <
swift-evolution at swift.org> wrote:

> 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/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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>


-- 
Brandon
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