[swift-evolution] [Proposal] Add floor() and ceiling() functions to FloatingPoint

[Pyry Jahkola]

> David Sweeris wrote:
> 
> I'm starting to come down from me earlier +1... Floor and ceiling are more functions than properties of a number, aren't they?

I agree with that. Having used various math libraries for decades now, I'd find it odd to find these as members of a floating-point type, especially so for the suggested in-place mutating variants. These tend to be function-like constructs (or various kinds of brackets) in mathematics too, just like trigonometric functions.

But since do we need these in the FloatingPoint protocol for generic algorithms, I'd suggest defining them as static members, and keeping state-of-art names (or close) where possible:

    protocol FloatingPoint {
      static func floor(_ value: Self) -> Self
      static func ceiling(_ value: Self) -> Self
      static func truncate(_ value: Self) -> Self
      static func round(_ value: Self) -> Self
    }

The top-level functions can them simply delegate to these counterparts:

    func floor<T : FloatingPoint>(_ value: T) -> T {
      return .floor(value)
    }

— Pyry