paste

import Foundation

@propertyWrapper public struct Percentage<Value: FloatingPoint> {
    
    private var storage: Value
    private let upperBound: Value
    
    public init(wrappedValue: Value, upperBound: Value = (1.0 as! Value)) {
        self.storage = wrappedValue
        self.upperBound = upperBound
    }
    
    public var wrappedValue: Value {
        get {
            switch storage {
            case ...0:
                return 0
            case 1...:
                return 1
            default:
                return storage
            }
        }
        
        set {
            assert((0...upperBound).contains(newValue),
                   "Percentage (\(newValue)) > \(upperBound), which is illegal.")
            storage = newValue
        }
    }
    
    public var projectedValue: Value {
        get {
            return storage
        }
        set {
            storage = newValue
        }
    }
    
}