Classes and Structs

Swift has both classes and structs. The key difference is that classes are reference types (shared identity) while structs are value types (independent copies). Swift prefers structs by default. Structs are ideal for simple data models — Point, Color, Rectangle. Classes are appropriate when you need reference semantics, inheritance, or Objective-C interoperability. Both can have properties, methods, initializers, and can conform to protocols.

Example

// Struct - value type
struct Point {
    var x: Double
    var y: Double

    // Memberwise initializer provided automatically
    func distanceTo(_ other: Point) -> Double {
        let dx = x - other.x
        let dy = y - other.y
        return (dx*dx + dy*dy).squareRoot()
    }

    // mutating required to modify stored properties
    mutating func move(by delta: Point) {
        x += delta.x
        y += delta.y
    }
}

var p1 = Point(x: 0, y: 0)
var p2 = p1          // independent copy
p2.x = 5
print(p1.x, p2.x)   // 0.0  5.0

// Class - reference type
class Counter {
    var count = 0
    func increment() { count += 1 }
    func reset() { count = 0 }
}

let c1 = Counter()
let c2 = c1          // same object
c2.increment()
print(c1.count)      // 1 (shared reference)

// Computed properties
struct Rectangle {
    var width: Double
    var height: Double
    var area: Double { width * height }
    var perimeter: Double { 2 * (width + height) }
}

HTML

Full Editor

Related Resources

Swift Reference

Complete tag & property list

Swift How-To Guides

Step-by-step practical guides

Swift Exercises

Practice what you've learned