Adds a prefix ^ operator which allows widening conversions between numeric types.

WideningOperatorExamples.swift

let i8 = Int8(42)
let i16 = Int16(42)
let i32 = Int32(42)
let i64 = Int64(42)

^i8 + i16

let f = Float(42.0)
let cgf = CGFloat(42.0)
let d = Double(42.0)

^f + d
^f + cgf
^cgf + d

d + ^i32

WideningOperatorImplementation.swift

prefix operator ^ {}

// Int8 widens to Int16, Int32, and Int64
prefix func ^ (x: Int8) -> Int16 {
    return Int16(x)
}

prefix func ^ (x: Int8) -> Int32 {
    return Int32(x)
}

prefix func ^ (x: Int8) -> Int64 {
    return Int64(x)
}

// Int16 widens to Int32 and Int64
prefix func ^ (x: Int16) -> Int32 {
    return Int32(x)
}

prefix func ^ (x: Int16) -> Int64 {
    return Int64(x)
}

// Int32 widens to Int64
prefix func ^ (x: Int32) -> Int64 {
    return Int64(x)
}

// Float widens to Double
prefix func ^ (x: Float) -> Double {
    return Double(x)
}

// Float <= CGFloat <= Double, so you can widen a Float to CGFloat and a CGFloat to Double
prefix func ^ (x: Float) -> CGFloat {
    return CGFloat(x)
}

prefix func ^ (x: CGFloat) -> Double {
    return Double(x)
}

// Int8 and Int16 widen to Float and CGFloat.
prefix func ^ (x: Int8) -> Float {
    return Float(x)
}

prefix func ^ (x: Int16) -> Float {
    return Float(x)
}

prefix func ^ (x: Int8) -> CGFloat {
    return CGFloat(x)
}

prefix func ^ (x: Int16) -> CGFloat {
    return CGFloat(x)
}

// Int8, Int16, and Int32 widen to Double
prefix func ^ (x: Int8) -> Double {
    return Double(x)
}

prefix func ^ (x: Int16) -> Double {
    return Double(x)
}

prefix func ^ (x: Int32) -> Double {
    return Double(x)
}

// Int64 and, by extension, Int can't safely widen to anything. (Well, I guess Float80, but nobody uses that.)