[swift-evolution] [Idea] Add `bounds` function to standard library

[Nicholas Maccharoli]

Georgios, Yes lets go with clamp for a name!

Pyry, Originally I thought of just adding a global function akin to `min`
and `max` but I am also
in favour of adding the above extension to `Comparable`.
I think having both the global function and the protocol extension for
`clamp` would be great.

- Nick


On Thu, Aug 25, 2016 at 9:37 PM, Pyry Jahkola <pyry.jahkola at iki.fi> wrote:

> On 25 Aug 2016, at 12:05, Nicholas Maccharoli wrote:
>
> I personally see merit in adding a function to bound the value of a
> variable within a range and think it would be simple to write with the
> existing implementations of `min` and `max` with something like:
>
>     public func bounds<T : Comparable>(value: T, _ lower: T, _ upper: T)
> -> T {
>         return max(lower, min(value, upper))
>     }
>
> Does this sound like something the community thinks would be worthwhile to
> add?
>
>
> I'd welcome that addition. In terms of function interface, I think we can
> do better than the 3-argument `clamp(x, min, max)` function that is seen
> in several math libraries.
>
> Our ***Range types already have a `clamped(to:)` member function, e.g. here's
> one for ClosedRange
> <https://developer.apple.com/reference/swift/closedrange/1779071-clamped>.
> It creates a new range constraining the receiver's bounds within the new
> bounds given as argument.
>
> I think the sensible thing would be to add a similar, and equally named,
> method to the Comparable protocol, taking in the ClosedRange<Self> to
> limit the value to:
>
>     extension Comparable {
>       public func clamped(to limits: ClosedRange<Self>) -> Self {
>         return self < limits.lowerBound ? limits.lowerBound
>              : self > limits.upperBound ? limits.upperBound
>              : self
>       }
>     }
>
>     (-0.1).clamped(to: 0 ... 1)       // 0.0
>     3.14.clamped(to: 0 ... .infinity) // 3.14
>     "foo".clamped(to: "a" ... "f")    // "f"
>     "foo".clamped(to: "a" ... "g")    // "foo"
>
> From my experience, I'd say it'd be most useful for clamping
> floating-point numbers and collection indices.
>
> — Pyry
>
>
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