HashableObjects.swift

struct Person {
  var name:String
}

let leo = Person(name: "Leo")
let nicole = Person(name: "Nicole")
let leonardoButCalledLeo = Person(name: "Leo")
let ashton = Person(name: "Ashton")

extension Person: Equatable {
}

func == (lhs:Person, rhs: Person)-> Bool {
  return lhs.name == rhs.name
}

extension Person: Hashable {
  var hashValue: Int {
    return name.hashValue
  }
}


func findItemCountForArray<T:Hashable>(arr:[T]) -> [T: Int] {
  
  // 1
  var countDict = [T: Int]()
  
  for key in arr {
    // 2
    if countDict[key] == nil {
      countDict[key] = 0
    }
    // 3
    countDict[key]! += 1
  }
  
  return countDict
}


let arrayOfPeople = findItemCountForArray([leo,leonardoButCalledLeo,ashton,nicole])
// Result: [{name "Leo"}: 2, {name "Ashton"}: 1, {name "Nicole"}: 1]

assert(leo == nicole)
// Result: error

assert(leo == leonardoButCalledLeo)
// Good