[swift-evolution] [Proposal draft] Add `Clamp` function to standard library

[David Rönnqvist]

There is already a `clamped` function for clamping one range to another and I feel that this function should be consistent with that one. As I see it, it can either be consistent in that it takes a Range as its argument, or in being an extension to Range. Probably something like either one of these:

extension Comparable { // or something else?
    func clamped(to range: Range<Self>) -> Self 
}

extension Range { 
    func clamping(_ value: Bound) -> Bound
}

Involving a range is good because that means that ensuring that the bounds checking (lower < upper) is already taken care of.

I do feel that this a useful addition to the standard library. But it is purely additive, so it should wait until after Phase 1.

- David

Sent from my iPad

> On 2 Sep 2016, at 18:55, Nicholas Maccharoli via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Introduction
> 
> The aim of this proposal is to introduce clamp functionality to the swift standard library. The clamp function would take a value and a upper and lower bounds to clamp the value to, ensuring that the return value of the function is within the range specified by the upper and lower bounds. Swift-evolution thread: Discussion thread topic for that proposal
> 
> Motivation
> 
> The standard library already includes functionality for min and max but at the time of this writing there is no global function for clamp. Adding a clamp function would complement min and max really well and would also eliminate the need for developers to write their own clamp functionality.
> 
> Proposed solution
> 
> I propose that a global clamp function akin to min and max be added to the standard library.
> 
> Detailed design
> 
> The implementation of the global clamp function would be as follows:
> 
> public func clamp<T : Comparable>(value: T, _ lower: T, _ upper: T) -> T {
>   return max(lower, min(value, upper))
> }
> Impact on existing code
> 
> There are no impacts on existing code, this proposal is purely additive.
> 
> Alternatives considered
> 
> Aside from not making the additions that this proposal wishes to make to the standard library no other alternatives have been considered.
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