Playing around with the concept of "emptiable" values

Emptiable.swift

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

import Cocoa

protocol Emptiable {
    static var emptyValue: Self { get }
}

extension Emptiable where Self: Equatable {
    var nonEmptyValue: Self? {
        return self == Self.emptyValue ? nil : self
    }
}

extension Optional where Wrapped: Emptiable {
    var valueOrEmpty: Wrapped {
        return self ?? Wrapped.emptyValue
    }
}

extension Optional where Wrapped: Emptiable & Equatable {
    func nonEmptyValue(orDefault defaultValue: Wrapped) -> Wrapped {
        return self?.nonEmptyValue ?? defaultValue
    }
}

extension String: Emptiable {
    static let emptyValue = ""
}


var str1: String? = "Hello, playground"
var str2: String? = ""
var str3: String? = nil

str1?.nonEmptyValue // "Hello, playground"
str2?.nonEmptyValue // nil
str3?.nonEmptyValue // nil
let defaultString = "default"
str1.nonEmptyValue(orDefault: defaultString) // "Hello, playground"
str2.nonEmptyValue(orDefault: defaultString) // "default"
str3.nonEmptyValue(orDefault: defaultString) // "default"
str1.valueOrEmpty // "Hello, playground"
str2.valueOrEmpty // ""
str3.valueOrEmpty // ""