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iOS Object-Oriented Swift Complex Data Structures Adding Instance Methods

Ethan Tam
Ethan Tam
2,684 Points
Posted by Ethan Tam
Ethan Tam
2,684 Points

Can someone please tell me what I did wrong in this code challenge. I am really confused about methods.

I watched the video on methods multiple times but something is still not clicking. I certain questions but I don't know the material well enough to put into words.

structs.swift 
struct Person {
    let firstName: String
    let lastName: String

    func fullName (Name: Person) -> String {
        return firstName + " " + lastName
    }
}
Ethan Tam
Ethan Tam
2,684 Points
Ethan Tam
Ethan Tam
2,684 Points

I got the answer and completed the code challenge, but how come my code is wrong when I put Person as a parameter?

2 Answers

Jennifer Nordell
seal-mask
STAFF
.a{fill-rule:evenodd;}techdegree
Jennifer Nordell
Treehouse Teacher
Jennifer Nordell
.a{fill-rule:evenodd;}techdegree
Jennifer Nordell
Treehouse Teacher

Hi there, Ethan! I received your request for assistance and have worked to try and put together an answer for you. However, I'm not sure I understand exactly what you're not understanding (if that makes any sense). You are wondering why you shouldn't send in a Person, and I'm wondering why you would. I've thought about it a bit and the only scenario I can come up with to need to send in one instance of a Person to another would be if the method needs to act based on a separate instance of the object. So I've expanded upon this example to see where this might be applicable (if a little far-fetched). This might also clear up some understanding about "self" and what it means.

Here is my example:

struct Person {
  let firstName: String
  let lastName: String

  func fullName () -> String {
    return firstName + " " + lastName  // returns the full name of the current instance of the person
  }

  func greetOtherPerson(other: Person) {
      let greeting = "Hi there, \(other.firstName)!   My name is \(self.fullName())."   //Use the other person's name and give your own full name
      print(greeting)  // print the greeting
  }
}

let me = Person(firstName: "Jennifer", lastName: "Nordell")  // create an instance of Person with my name
let you = Person(firstName: "Ethan", lastName: "Tam")  // create an instance of Person with your name

me.greetOtherPerson(other: you)
//Output:  Hi there, Ethan!  My name is Jennifer Nordell.

you.greetOtherPerson(other: me)
//Output:  Hi there, Jennifer!  My name is Ethan Tam.

This is, of course, buildable and runnable in a Playground :smiley: Other than giving this expanded example, I'm not sure what else I can add, but let me know if you need more clarification! :sparkles:

Ethan Tam
Ethan Tam
2,684 Points
Ethan Tam
Ethan Tam
2,684 Points

Thank you so much for your insight. I guess the most confusing part is that I don't understand how a function can produce something when it doesn't take in anything. How can a function have no parameter?

Jennifer Nordell
seal-mask
.a{fill-rule:evenodd;}techdegree
Jennifer Nordell
Treehouse Teacher
Jennifer Nordell
.a{fill-rule:evenodd;}techdegree
Jennifer Nordell
Treehouse Teacher

Not every function needs outside information. A good portion of them do, yes, but you can make a function that simply displays something.

function sayHi() {
   print("Hello Ethan!  Pleased to meet you!")
}

sayHi()

But the problem with these functions (generally speaking) are that they do something very specific and very limited as they generally do something very specific with either something hard-coded or something available in the global scope.

Hope this helps! :sparkles:

edited for addition information

In the code in this challenge a struct is used. Structs come with their own default initializer which means that the firstName and lastName constants are automatically accessible to the function without them being passed in.

Michael Hulet
Michael Hulet
47,912 Points
Michael Hulet
Michael Hulet
47,912 Points

To clarify a bit, in the case of this question, the fullName function is a method. All methods are functions, but not all functions are methods. If the function is declared on a class, struct, or enum, it's a method, but if it stands all by itself, it's just a function. Methods are all given one parameter, even if you declare none. That parameter is self inside the method. When you compile the code to pass this challenge, it's actually turned into a low-level C call that makes your method actually look something like this:

func fullName(self: Person) -> String{
    return self.firstName + " " + self.lastName
}

iOS will eventually call your method like this:

var current: Person // Assume this variable is equal to the current Person instance that's being operated on
fullName(self: current)

A good concrete example of how this is implemented is how Python methods work. In Python, you have to write the self keyword for the method to work. This is the above class, but written in Python:

class Person:
    def __init__(self, first_name, last_name):
        self.first_name = first_name
        self.last_name = last_name

    def full_name(self):
        return self.first_name + " " + self.last_name

See how Python makes you write out the self keyword every time? It works exactly the same in Swift under the hood, but Swift doesn't make you write self every time