Unwrap convenience operator

UnwrapOrDefault.swift

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

// NOTE: Now that Swift has ?? operator, this gist is mostly obsolete.

protocol HasNaturalDefault
    { class var naturalDefault:Self {get} }

operator postfix  ~! {}

operator infix ~! {associativity none precedence 170}

@postfix func ~! <T:HasNaturalDefault> (lhs: T?) -> T
    { return lhs ? lhs! : T.naturalDefault }

@infix func ~! <T> (lhs: T?, rhs: T) -> T
    { return lhs ? lhs! : rhs }

extension Array : HasNaturalDefault {
    static var naturalDefault:Array { return [ ] }
}

extension Bool: HasNaturalDefault {
    static var naturalDefault:Bool { return false }
}

extension Dictionary : HasNaturalDefault {
    static var naturalDefault:Dictionary { return [ : ] }
}

extension Double: HasNaturalDefault {
    static var naturalDefault:Double { return 0.0 }
}

extension Int: HasNaturalDefault {
    static var naturalDefault:Int { return 0 }
}

extension String: HasNaturalDefault {
    static var naturalDefault:String { return "" }
}

// Samples with optionals:

var a:[Int]?, b:Bool?, d:[String:Int]?, x:Double?, i:Int?, s:String?

a~!
b~!
d~!
x~!
i~!
s~!

a~![1,2,3]
b~!true
d~!["Key":1]
x~!3.1415927
i~!666
s~!"Joe"

// Works with implicitly unwrapped optionals, too:

var a1:[Int]!, b1:Bool!, d1:[String:Int]!, x1:Double!, i1:Int!, s1:String!

a1~!
b1~!
d1~!
x1~!
i1~!
s1~!

a1~![1,2,3]
b1~!true
d1~!["Key":1]
x1~!3.1415927
i1~!666
s1~!"Joe"

// Even this works:
return x~!2.0*y~!-2.0/z~!2.0
// But It is better to write as:
return x~!2.0 * y~!-2.0 / z~!2.0