[swift-evolution] [Accepted] SE-0113: Add integral rounding functions to FloatingPoint

[Pyry Jahkola]

I think one more thing needs clarification. Shouldn't the "defaulted" `rounded()` and `round()` be defined as protocol extension methods *without* the possibility to override the default rounding mode in a conforming type? Like so:

    public protocol FloatingPoint {
      ...
      func rounded(_ rule: RoundingRule) -> Self
      mutating func round(_ rule: RoundingRule)
    }

    public extension FloatingPoint {
      public func rounded() -> Self {
        return rounded(.toNearestOrAwayFromZero)
      }
      public mutating func round() {
        round(.toNearestOrAwayFromZero)
      }
    }

I would find it quite surprising if some type conforming to FloatingPoint rounded differently by default than the others.

— Pyry

> Chris Lattner wrote:
> 
> Since protocol requirements cannot currently have default arguments, the desired behavior should be achieved with two overloads of each operation:
> 
> protocol FloatingPoint {
>  ...
>  /// Returns a rounded representation of `self`, according to the specified rounding rule.
>  func rounded() -> Self
>  func rounded(_ rule: RoundingRule) -> Self
> 
>  /// Mutating form of `rounded`.
>  mutating func round()
>  mutating func round(_ rule: RoundingRule)
> }
> 
> Where the no argument cases can be implemented with a protocol extension that forwards to the single-argument versions.