Structs and Classes

Struct Methods

Methods are functions attached to a type and called on an instance.

Call behavior on a value

width
struct_methods.swift
Replay: real traced execution (multi-file project)
struct Rectangle {
    let width: Int
    let height: Int

    func area() -> Int {
        return width * height
    }
}

let width = 6
let rectangle = Rectangle(width: width, height: 4)
let area = rectangle.area()

print("width=\(width)")
print("area=\(area)")

struct Rectangle {
    let width: Int
    let height: Int

    func area() -> Int {
        return width * height
    }
}

let width = 3
let rectangle = Rectangle(width: width, height: 4)
let area = rectangle.area()

print("width=\(width)")
print("area=\(area)")

struct Rectangle {
    let width: Int
    let height: Int

    func area() -> Int {
        return width * height
    }
}

let width = 9
let rectangle = Rectangle(width: width, height: 4)
let area = rectangle.area()

print("width=\(width)")
print("area=\(area)")

  1. width ← 6, rectangle ← Rectangle(width: 6, height: 4)

    10let width→ 6 = 6  //@width=3, 911let rectangle→ Rectangle(width: 6, height: 4) = Rectangle(width: width6, height: 4)12let area = rectangleRectangle(width: 6, height: 4).area()

  2. func area() -> Int

    5func area() -> Int {6    return width6 * height47}

  3. area ← 24

    11let rectangle = Rectangle(width: width, height: 4)12let area→ 24 = rectangleRectangle(width: 6, height: 4).area()1314print("width=\(width6)")15print("area=\(area24)")
    outputwidth=6
area=24

  1. width ← 3, rectangle ← Rectangle(width: 3, height: 4)

    10let width→ 3 = 311let rectangle→ Rectangle(width: 3, height: 4) = Rectangle(width: width3, height: 4)12let area = rectangleRectangle(width: 3, height: 4).area()

  2. func area() -> Int

    5func area() -> Int {6    return width3 * height47}

  3. area ← 12

    11let rectangle = Rectangle(width: width, height: 4)12let area→ 12 = rectangleRectangle(width: 3, height: 4).area()1314print("width=\(width3)")15print("area=\(area12)")
    outputwidth=3
area=12

  1. width ← 9, rectangle ← Rectangle(width: 9, height: 4)

    10let width→ 9 = 911let rectangle→ Rectangle(width: 9, height: 4) = Rectangle(width: width9, height: 4)12let area = rectangleRectangle(width: 9, height: 4).area()

  2. func area() -> Int

    5func area() -> Int {6    return width9 * height47}

  3. area ← 36

    11let rectangle = Rectangle(width: width, height: 4)12let area→ 36 = rectangleRectangle(width: 9, height: 4).area()1314print("width=\(width9)")15print("area=\(area36)")
    outputwidth=9
area=36

Follow the Method

  1. width starts as 6.
  2. rectangle stores width 6 and height 4.
  3. rectangle.area() calls the method on that rectangle.
  4. The method returns width * height.
  5. area becomes 24. | width | height | area | | --- | --- | --- | | 6 | 4 | 24 | | 3 | 4 | 12 | | 9 | 4 | 36 |
methods A method can read the instance's properties and return a calculated result.

Exercise: struct_methods.swift

Reproduce width=6 and area=24, then use the pinned width variants 3 and 9 to predict area=12 and area=36.