Add Strideble to ConstraintPriority

ConstraintPriorityPlayground.swift

//: Playground - noun: a place where people can play

import Foundation

public struct ConstraintPriority : ExpressibleByFloatLiteral, Equatable, Strideable {
    public typealias FloatLiteralType = Float
    public typealias Stride = Float

    public let value: Float

    public init(floatLiteral value: Float) {
        self.value = value
    }

    public init(_ value: Float) {
        self.value = value
    }

    public static var required: ConstraintPriority {
        return 1000.0
    }

    public static var high: ConstraintPriority {
        return 750.0
    }

    public static var low: ConstraintPriority {
        return 250.0
    }

    public static func ==(lhs: ConstraintPriority, rhs: ConstraintPriority) -> Bool {
        return lhs.value == rhs.value
    }

    public func advanced(by n: Float) -> ConstraintPriority {
        return ConstraintPriority(floatLiteral: value + n)
    }

    public func distance(to other: ConstraintPriority) -> Float {
        return other.value - value
    }
}

func priority(_ p: ConstraintPriority) -> Float {
    return p.value
}

priority(600.0)
priority(.high)
priority(.high + 1)
priority(.low - 1)