isBlank.swift

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

import UIKit

extension String {
    var isBlank: Bool {
        return trimmingCharacters(in: CharacterSet.whitespaces).isEmpty
    }
}

protocol StringProvider {
    var getString: String { get }
}

extension String: StringProvider {
    var getString: String {
        return self
    }
}

extension Optional where Wrapped: StringProvider {
    var isBlank: Bool {
        return self?.getString.isBlank ?? true
    }
}

var s1: String? = nil
var s2: String? = ""
var s3: String? = "   "
var s4: String? = "car"

s1.isBlank
s2.isBlank
s3.isBlank
s4.isBlank


// isBlank is the Rails way.  A more Swift way to do it is to consider how it is used
// at call site.  We want to operate on a filled in text string. Make a property
// filled that returns the string or nil if the string is empty.

extension String {
    var filled: String? {
        return trimmingCharacters(in: .whitespaces).isEmpty ? nil : self
    }
}

// what about optionals?... for that we can just use standard optional chaining! (aka flatMap)

let username = UILabel()
username.text = "ray"
let password = UILabel()
password.text = "secret"

func login(username: UILabel, password: UILabel) {
    guard let username = username.text?.filled else {
        print("no username")
        return
    }
    
    guard let password = password.text?.filled else {
        print("no password")
        return
    }

    print (username, password)
}

login(username: username, password: password)