A little test to make a Percent struct wrapping a Float (could be generic Float/Double)

Percent.swift

import Foundation

public struct Percent {
    private var _val: Float
}

public func == (left: Percent, right: Percent) -> Bool {
    return left._val == right._val
}

public func < (left: Percent, right: Percent) -> Bool {
    return left._val < right._val
}

public prefix func -(x: Percent) -> Percent {
    return Percent(floatLiteral: -x._val)
}

public func -(lhs: Percent, rhs: Percent) -> Percent {
    return Percent(floatLiteral: lhs._val - rhs._val)
}


extension Percent: Comparable {
    
}

extension Percent: Hashable {
    public var hashValue: Int {
        return _val.hashValue
    }
}

extension Percent: IntegerLiteralConvertible {
    public init(integerLiteral value: Int) {
        _val = Float(value)
    }
}

extension Percent: FloatLiteralConvertible {
    public init(floatLiteral value: Float) {
        _val = Float(value)
    }
}

extension Percent: SignedNumberType {
}

extension Percent: AbsoluteValuable {
    public static func abs(x: Percent) -> Percent {
        return Percent(floatLiteral: Float.abs(x._val))
    }
}