[swift-evolution] [draft] Add `clamped(to:)` to the stdlib
Nicholas Maccharoli
nmaccharoli at gmail.com
Wed Mar 15 21:35:12 CDT 2017
Here is the updated version of the proposal:
https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/NNNN-add-clamp-function.md
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 provided Range. 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 function to limit a value to a given
range and was disappointed it was not part of the standard library.
There already exists an extension to CountableRange in the standard library
implementing clamped(to:) that will limit the calling range to that of the
provided range, so having the same functionality but just for types that
conform to the Comparable protocol would be conceptually consistent.
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, perhaps one example of this coming in
handy would be to limit the result of some calculation between two
acceptable numerical limits, say the bounds of a coordinate system.
<https://github.com/Nirma/swift-evolution/blob/clamp_function/proposals/NNNN-add-clamp-function.md#proposed-solution>Proposed
solution
The proposed solution is to add a clamped(to:) function to the Swift
Standard Library as an extension to Comparable and Strideable. The function
would return a value within the bounds of the provided range, if the value
clamped(to:) is being called on falls within the provided range then the
original value would be returned. If the value was less or greater than the
bounds of the provided range then the respective lower or upper bound of
the range would be returned.
It does not make sense to call clamped(to:) with an empty range, therefore
calling clamped(to:) and passing an empty range like foo.clamped(to:
0..<0) would
result in a fatal error.
Given a clamped(to:) function existed it could be called in the following
way, yielding the results in the adjacent comments:
let 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 {
if range.isEmpty { fatalError("Can't form Range with
upperBound < lowerBound") }
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 Thu, Mar 16, 2017 at 11:33 AM, Nicholas Maccharoli <nmaccharoli at gmail.com
> wrote:
> Right, there were a few things missing!
> Thanks so much for pointing them out everyone.
>
> Dave - Great idea! I have updated the motivation section section as you
> suggested!
>
> Neil - Yes I also think the wording could be a bit better but since the
> word `clamped` is already being used
> I thought I would keep it consistent.
>
> Sean - Looks as if its a term of art to me as well.
>
> Nate,
>
> Good catch! Yes I also thing clamping on an empty range should be a fatal
> error as well.
> An empty range is impossible to create with `ClosedRange` so I left the
> implementation
> of that alone, but it is possible with `Range` so I updated the extension
> on `Strideable` like so:
>
> extension Strideable where Stride: Integer {
> func clamped(to range: Range<Self>) -> Self {
> if range.isEmpty { fatalError("Can't form Range with upperBound < lowerBound") }
> return clamped(to: range.lowerBound...(range.upperBound - 1))
> }
> }
>
>
>
>
> Jaden,
>
> Yeah I think a simple `if` check would work as well.
>
>
> On Thu, Mar 16, 2017 at 10:19 AM, Jaden Geller <jaden.geller at gmail.com>
> wrote:
>
>>
>> On Mar 15, 2017, at 12:40 PM, Nate Cook via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>
>> Hi Nick,
>>
>> I think this might have come up in an earlier thread, but clamped(to:)
>> with a half-open range argument brings up the question of how to clamp to
>> an empty range. As proposed, the implementation of this method would result
>> in an error when passed an empty range:
>>
>> foo.clamped(to: 0..<0)
>> // fatal error: Can't form Range with upperBound < lowerBound
>>
>>
>> Ahh, good catch! The implementation ought to add something like:
>>
>> guard !range.isEmpty else { fatalError("Cannot clamp to an empty range")
>> }
>>
>> I don’t think that this is problematic. Ideally we could express in the
>> type-system that the range must not be empty, but it is definitely not
>> worthwhile creating a `NonemptyRange` type.
>>
>>
>> Is that the desired behavior? Providing documentation for both new
>> methods would help make it clear what the expected functionality is.
>>
>> Thanks!
>> Nate
>>
>>
>> On Mar 13, 2017, at 9:16 PM, Nicholas Maccharoli via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>
>> Swift-Evolution,
>>
>> After considering the indispensable feedback from the community here is a
>> slightly more polished draft.
>>
>> If anyone is interested the draft can be downloaded here:
>> https://github.com/Nirma/swift-evolution/blob/clamp_function
>> /proposals/NNNN-add-clamp-function.md
>>
>> Thank you so much,
>>
>> - 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:
>>
>> let 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.
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>
>>
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>
>>
>>
>
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