== vs === — what's the difference?

Junior PRO

The idea

• == compares values. Defined by the Equatable protocol; for your own types you decide what "equal" means (all fields, only id, case-insensitive).
• === compares identity: whether two references point to the same object in memory. Defined only for AnyObject, i.e. classes (and class-bound protocols). For structs, enums and tuples === does not exist.

final class Node: Equatable {
    let value: Int
    init(_ value: Int) { self.value = value }
    static func == (l: Node, r: Node) -> Bool { l.value == r.value }
}

let a = Node(1), b = Node(1), c = a
print(a == b, a === b, a === c)   // true false true