[swift-evolution] [draft] Add `clamped(to:)` to the stdlib

Nicholas Maccharoli nmaccharoli at gmail.com
Sun Mar 12 20:21:42 CDT 2017 

Jaden,

Awesome feedback, and yes I totally agree that support for Half-Open ranges
would be awesome so I updated the proposal adding your code and also
updating the example code in the motivation to include the Half-Open range
variant and updating the "Alternatives Considered" section to accurately
reflect that no alternatives have been considered.

As for the implementation, an implementation using min-max would also be
fine but I thought although a little verbose using an if-if-else-else
clause would read a little easier.

I personally think either way is great,  just thought I would try an
alternative.

- Nick

Add clamp(to:) to the stdlib

   - Proposal: SE-NNNN
   <https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/NNNN-filename.md>
   - Authors: Nicholas Maccharoli <https://github.com/Nirma>
   - Review Manager: TBD
   - Status: Awaiting review

*During the review process, add the following fields as needed:*

   - Decision Notes: Rationale
   <https://lists.swift.org/pipermail/swift-evolution/>, Additional
   Commentary <https://lists.swift.org/pipermail/swift-evolution/>
   - Bugs: SR-NNNN <https://bugs.swift.org/browse/SR-NNNN>, SR-MMMM
   <https://bugs.swift.org/browse/SR-MMMM>
   - Previous Revision: 1
   <https://github.com/apple/swift-evolution/blob/...commit-ID.../proposals/NNNN-filename.md>
   - Previous Proposal: SE-XXXX
   <https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/XXXX-filename.md>

<https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/NNNN-add-clamp-function.md#introduction>
Introduction

This proposal aims to add functionality to the standard library for
clamping a value to a ClosedRange. The proposed function would allow the
user to specify a range to clamp a value to where if the value fell within
the range, the value would be returned as is, if the value being clamped
exceeded the upper or lower bound in value the value of the boundary the
value exceeded would be returned.

Swift-evolution thread: Add a clamp function to Algorithm.swift
<https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20170306/thread.html#33674>
<https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/NNNN-add-clamp-function.md#motivation>
Motivation

There have been quite a few times in my professional and personal
programming life where I reached for a clampedfunction and was disappointed
it was not part of the standard library.

Having functionality like clamped(to:) added to Comparable as a protocol
extension would benefit users of the Swift language who wish to guarantee
that a value is kept within bounds.
<https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/NNNN-add-clamp-function.md#proposed-solution>Proposed
solution

The solution proposed is simply that there be a clamped(to:) function added
to the Swift Standard Library. The function would behave much like its name
describes.

Given a clamped(to:) function existed it could be called in the following
way, yielding the results in the adjacent comments:

var foo = 100
// Closed range variant
foo.clamped(to: 0...50) // 50foo.clamped(to: 200...300) //
200foo.clamped(to: 0...150) // 100// Half-Open range variant
foo.clamped(to: 0..<50) // 49foo.clamped(to: 200..<300) //
200foo.clamped(to: 0..<150) // 100

<https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/NNNN-add-clamp-function.md#detailed-design>Detailed
design

The implementation of clamped(to:) that is being proposed is composed of
two protocol extensions; one protocol extension on Comparable and another
on Strideable.

The implementation for clamped(to:) as an extension to Comparable accepting
a range of type ClosedRange<Self>would look like the following:

extension Comparable {
    func clamped(to range: ClosedRange<Self>) -> Self {
        if self > range.upperBound {
            return range.upperBound
        } else if self < range.lowerBound {
            return range.lowerBound
        } else {
            return self
        }
    }
}

The implementation of clamped(to:) as an extension on Strideable would be
confined to cases where the stride is of type Integer. The implementation
would be as follows:

extension Strideable where Stride: Integer {
    func clamped(to range: Range<Self>) -> Self {
        return clamped(to: range.lowerBound...(range.upperBound - 1))
    }
}

<https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/NNNN-add-clamp-function.md#source-compatibility>Source
compatibility

This feature is purely additive; it has no effect on source compatibility.
<https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/NNNN-add-clamp-function.md#effect-on-abi-stability>Effect
on ABI stability

This feature is purely additive; it has no effect on ABI stability.
<https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/NNNN-add-clamp-function.md#effect-on-api-resilience>Effect
on API resilience

The proposed function would become part of the API but purely additive.
<https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/NNNN-add-clamp-function.md#alternatives-considered>Alternatives
considered

Aside from doing nothing, no other alternatives were considered.

On Mon, Mar 13, 2017 at 7:47 AM, Jaden Geller <jaden.geller at gmail.com>
wrote:

> You definitely ought to add “do nothing” to the alternative considered
> section. Also, any reason you didn’t implement `clamped` in terms of `min`
> and `max`?
>
> On Mar 12, 2017, at 10:16 AM, Nicholas Maccharoli via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> ​Swift-Evolution.
>
> This is a draft of a proposal adding `clamped(to:)` as an extension on
> `Comparable`.
> For now I have only included a version of the `clamped(to:)` function that
> accepts `ClosedRange` but if the community decided that it is feasible to
> add a version that takes half open ranges I would also love to include that
> as well in this proposal.
>
> That you so much for the feedback so far and I am looking forward
> to the community's feedback on this draft.
>
> - Nick
>
>
> Add clamp
> ​ed​
> (to:) to the stdlib
>
>    - Proposal: SE-NNNN
>    <https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/NNNN-filename.md>
>    - Authors: Nicholas Maccharoli <https://github.com/Nirma>
>    - Review Manager: TBD
>    - Status: Awaiting review
>
> *During the review process, add the following fields as needed:*
>
>    - Decision Notes: Rationale
>    <https://lists.swift.org/pipermail/swift-evolution/>, Additional
>    Commentary <https://lists.swift.org/pipermail/swift-evolution/>
>    - Bugs: SR-NNNN <https://bugs.swift.org/browse/SR-NNNN>, SR-MMMM
>    <https://bugs.swift.org/browse/SR-MMMM>
>    - Previous Revision: 1
>    <https://github.com/apple/swift-evolution/blob/...commit-ID.../proposals/NNNN-filename.md>
>    - Previous Proposal: SE-XXXX
>    <https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/XXXX-filename.md>
>
>
> <https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/NNNN-add-clamp-function.md#introduction>
> Introduction
>
> This proposal aims to add functionality to the standard library for
> clamping a value to a ClosedRange. The proposed function would allow the
> user to specify a range to clamp a value to where if the value fell within
> the range, the value would be returned as is, if the value being clamped
> exceeded the upper or lower bound in value the value of the boundary the
> value exceeded would be returned.
>
> Swift-evolution thread: Add a clamp function to Algorithm.swift
> <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20170306/thread.html#33674>
>
> <https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/NNNN-add-clamp-function.md#motivation>
> Motivation
>
> There have been quite a few times in my professional and personal
> programming life where I reached for a clampedfunction and was
> disappointed it was not part of the standard library.
>
> Having functionality like clamped(to:) added to Comparable as a protocol
> extension would benefit users of the Swift language who wish to guarantee
> that a value is kept within bounds.
>
> <https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/NNNN-add-clamp-function.md#proposed-solution>Proposed
> solution
>
> The solution proposed is simply that there be a clamped(to:) function
> added to the Swift Standard Library. The function would behave much like
> its name describes.
>
> Given a clamped(to:) function existed it could be called in the following
> way, yielding the results in the adjacent comments:
>
> var foo = 100
> foo.clamp(to: 0...50) // 50foo.clamp(to: 200...300) // 200foo.clamp(to: 0...150) // 100
>
>
> <https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/NNNN-add-clamp-function.md#detailed-design>Detailed
> design
>
> The implementation for clamped(to:) as an extension to Comparable accepting
> a range of type ClosedRange<Self>would look like the following:
>
> extension Comparable {
>     func clamped(to range: ClosedRange<Self>) -> Self {
>         if self > range.upperBound {
>             return range.upperBound
>         } else if self < range.lowerBound {
>             return range.lowerBound
>         } else {
>             return self
>         }
>     }
> }
>
>
> <https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/NNNN-add-clamp-function.md#source-compatibility>Source
> compatibility
>
> This feature is purely additive; it has no effect on source compatibility.
>
> <https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/NNNN-add-clamp-function.md#effect-on-abi-stability>Effect
> on ABI stability
>
> This feature is purely additive; it has no effect on ABI stability.
>
> <https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/NNNN-add-clamp-function.md#effect-on-api-resilience>Effect
> on API resilience
>
> The proposed function would become part of the API but purely additive.
>
> <https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/NNNN-add-clamp-function.md#alternatives-considered>Alternatives
> considered
> clamped(to:) could be made a global function like min and max but a
> protocol extension seems like a better choice.​
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
>
>
>
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