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iOS Object-Oriented Swift Properties Computed Properties

Difference between a method and a Computed Property?

So, if we could return a value using both a method and a computed property, what's the difference between them (besides that one is a method, the other one is not) and which one should we use in what particular cases?

2 Answers

Greg Kaleka
Greg Kaleka
39,021 Points

Methods are things the object can do, while properties are things about the object. A computed property is just a way to make it easier to get to an attribute of an object.

For example, imagine you had a Person class, which had a yearOfBirth property. You want to figure out how old the person is. Do you use a method to calculate it or set a calculated property?

Well, we're trying to figure out someone's age, so I think it makes the most sense to set a calculated property. We could do this easily, and refer to dani.age later on to get your age.

Here's an example:

class Person {
   let name: String
   let yearOfBirth: Int
   var age: Int {
      return 2015 - yearOfBirth  // note, this is simplified. I would probably use NSDate instead to really calculate the age, and have it update itself as time went on

   init(name: String, yearOfBirth: Int){
      self.name = name
      self.yearOfBirth= yearOfBirth

let dani = Person(name: "Dani", yearOfBirth: 1900)

dani.name // "Dani"
dani.yearOfBirth // 1900
dani.age // 115

Gosh, you're old! ;-)

Make sense?

Yes, it does make sense! Thanks!