[swift-evolution] protocol-oriented integers (take 2)

[Ben Rimmington]

<https://gist.github.com/moiseev/62ffe3c91b66866fdebf6f3fcc7cad8c>

	public protocol Arithmetic {
	  init?<T : BinaryInteger>(exactly source: T)
	}

	public protocol BinaryInteger : Arithmetic {
	  init?<T : FloatingPoint>(exactly source: T)
	}

Should the `init?(exactly:)` initializers belong to the same protocol?
Would this allow generic conversions between integer and floating-point types?
For example, a failable `numericCast` function.

-- Ben