1// Java
2public class Person {
3    private String name;
4    private int age;
5
6    public Person(String name, int age) {
7        this.name = name;
8        this.age = age;
9    }
10
11    @Override
12    public String toString() {
13        return "Person(name=" + name + ", age=" + age + ")";
14    }
15}
16
17System.out.println(new Person("Alice", 30));
18// Person(name=Alice, age=30)

1// Swift equivalent
2struct Person: CustomStringConvertible {
3    let name: String
4    let age: Int
5
6    var description: String {
7        return "Person(name=\(name), age=\(age))"
8    }
9}
10
11print(Person(name: "Alice", age: 30))
12// Person(name=Alice, age=30)

1struct Point {
2    let x: Double
3    let y: Double
4}
5
6let p = Point(x: 3.0, y: 4.0)
7print(p)
8// Point(x: 3.0, y: 4.0)  — Swift generates a default description for structs
9
10// String interpolation also uses the default
11let msg = "Location: \(p)"
12print(msg)
13// Location: Point(x: 3.0, y: 4.0)

1struct Matrix: CustomStringConvertible, CustomDebugStringConvertible {
2    let rows: Int
3    let cols: Int
4    let data: [[Double]]
5
6    // Used by print() and string interpolation
7    var description: String {
8        return "Matrix(\(rows)x\(cols))"
9    }
10
11    // Used by debugPrint() and the debugger (po command)
12    var debugDescription: String {
13        let content = data.map { row in
14            row.map { String(format: "%.2f", $0) }.joined(separator: ", ")
15        }.joined(separator: "\n  ")
16        return "Matrix(\(rows)x\(cols)) [\n  \(content)\n]"
17    }
18}
19
20let m = Matrix(rows: 2, cols: 2, data: [[1, 2], [3, 4]])
21print(m)
22// Matrix(2x2)
23
24debugPrint(m)
25// Matrix(2x2) [
26//   1.00, 2.00
27//   3.00, 4.00
28// ]

1// String(describing:) — uses description if available
2let p = Person(name: "Alice", age: 30)
3let s = String(describing: p)
4// "Person(name=Alice, age=30)"
5
6// String(reflecting:) — uses debugDescription if available
7let d = String(reflecting: p)
8
9// String interpolation — calls description automatically
10let msg = "User: \(p)"
11
12// Converting numbers and primitives
13let n = 42
14String(n)           // "42"
15String(3.14)        // "3.14"
16String(true)        // "true"
17
18// Formatting numbers
19String(format: "%.2f", 3.14159)   // "3.14"
20String(format: "%05d", 42)        // "00042"

1enum Direction: CustomStringConvertible {
2    case north, south, east, west
3
4    var description: String {
5        switch self {
6        case .north: return "North"
7        case .south: return "South"
8        case .east:  return "East"
9        case .west:  return "West"
10        }
11    }
12}
13
14print(Direction.north)  // "North"
15
16// Without CustomStringConvertible, enums print their case name
17enum Color { case red, green, blue }
18print(Color.red)  // "red"

1struct Task: CustomStringConvertible {
2    let title: String
3    let done: Bool
4
5    var description: String {
6        return "\(done ? "✓" : "○") \(title)"
7    }
8}
9
10let tasks = [
11    Task(title: "Write code", done: true),
12    Task(title: "Write tests", done: false),
13    Task(title: "Deploy", done: false)
14]
15
16print(tasks)
17// [✓ Write code, ○ Write tests, ○ Deploy]
18
19// Arrays call description on each element when printing