What are value types and reference types in Swift?

Swift has two fundamental categories of types that behave differently when assigned or passed: Value types (struct, enum, tuple) — each instance keeps a unique copy. Assigning or passing creates a new copy: struct Point { var x: Int; var y: Int } var p1 = Point(x: 1, y: 2) var p2 = p1 // Independent copy p2.x = 10 print(p1.x) // 1 -- unchanged print(p2.x) // 10. Swift uses Copy-On-Write (COW) for standard library value types (Array, String, Dictionary) — the copy only happens when a mutation occurs, making copies cheap until modification. Reference types (class, actor) — multiple references to the same instance. Assigning copies the reference, not the object: class Counter { var count = 0 } let c1 = Counter() let c2 = c1 // Same object! c2.count += 1 print(c1.count) // 1 -- affected!. When to use each: use struct (value type) for: data models, most custom types in Swift — structs with no inheritance, thread safety by default, value semantics; use class (reference type) when: you need inheritance, identity matters (comparing if two references point to the same object), Objective-C interoperability, shared mutable state. Swift standard library types (Array, String, Dictionary, Int, Bool) are all value types (structs). SwiftUI heavily uses structs for Views.