functions and structs

Basics

• A struct is something
• A function does something. You give it some parameters, and based on that it returns something, or performs some action

So a struct represents something. So, say you're trying to create a graph. Well, with a graph you have to create points (x,y). How would you do that? Or, really you should ask, "How would I represent this?" Answer: Struct

struct Point {
   var x: Int
   var y: Int
}

Now, can you do this with functions?

func point(x: Int, y: Int) {
  // What to do in here?
  // Well the point of a function is to do something, so it doesn't apply here.
  // We're not trying to DO anything. We just want to represent something
  // See, it's hard to represent even something as simple as a point with functions
}

It makes sense why this doesn't work, and to show this let's do a task: Create a variable and print the x value (Using our previous definition of struct Point)

// This calls the structs' implied initializer method. It creates a struct.
// Yes it looks like a function call, but that's with all initializers.
  var origin = Point(x: 0, y: 0) 
  print(origin.x)

Now let's try to do this with a function (Using our previous definition of func point

  var origin = point(x: 0, y:0) // Okay, they look identical so far.....
  print(origin.x) // ERROR
  // See, there is no .x associated with this because a function doesn't have properties. Structs do!
  // This really doesn't make sense. This function doesn't even return anything, so the first line will be an error as well.

So now we see where structs thrive..... What about functions? Well, let's stick to our point example. What if we want to calculate the slope between two points? Now look at that sentence.... I used a verb calculate. This DOES something. So a function will be used here:

  func slope(point1: Point, point2: Point) -> Int {
    let x1 = point1.x
    let y1 = point1.y

    let x2 = point2.x
    let y2 = point2.y

    return (y2 - y1) / (x2 - x1)
}

This makes sense, and is very easy to do. Can we do this with structs!?

Well, you shouldn't! When you're trying to DO something, use functions. Calculating the slope is doing something.