Structs

Structs are Swift’s preferred way to model most data—value semantics, automatic memberwise initializers, and copy-on-write performance. Unlike Java classes, structs are copied by assignment.

Defining and using structs

struct Point {
    var x: Double
    var y: Double

    func distance(from other: Point) -> Double {
        let dx = x - other.x
        let dy = y - other.y
        return (dx*dx + dy*dy).squareRoot()
    }
}

var a = Point(x: 0, y: 0)
var b = a
b.x = 3
print(a.x)  // still 0

Compared to Kotlin data classes

Kotlin data class on JVM is reference-typed; Swift structs are true value types—important for reasoning about mutation and threading.

Important interview questions and answers

1. Q: Struct vs class?
   A: Structs are value types copied on assignment; classes are reference types with ARC—prefer structs for models unless you need inheritance or shared identity.
2. Q: Can structs have methods?
   A: Yes—methods, computed properties, and protocol conformance are all supported.

Self-check

1. What happens to a when you mutate copy b?
2. When should you choose a class over a struct?

Tip: Default to structs for models—value semantics simplify reasoning vs reference types.