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

[Nicholas Maccharoli]

Tim,

The protocol extension alone would be sufficient, but for as long as the
global functions
`min` and `max` are still around I thought adding a global clamp function
would make
for good symmetry.

I'll write a small draft proposal to illustrate my idea a little better.

What does the community think?

- Nick



On Tue, Aug 30, 2016 at 2:25 AM, Tim Vermeulen <tvermeulen at me.com> wrote:

> What would the point of a free function be if you already have a protocol
> extension?
>
> > 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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