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Comparable / Hashable / Equatable

Comparable / Hashable / Equatable

Swift provides standard protocols — Equatable, Comparable, and Hashable — that enable equality checks, ordering comparisons, and hashing for your types.

Protocol Overview

Protocol	Description
Equatable	Enables equality comparison using the == operator.
Comparable	Inherits from Equatable and enables ordering with the < operator. The <= / > / >= operators are synthesized automatically.
Hashable	Inherits from Equatable and allows the type to be used as a key in Set or Dictionary.
Identifiable	Requires a unique id property. Commonly used with SwiftUI.

Sample Code

// Equatable: equality check
struct Point: Equatable {
    var x: Double
    var y: Double

    // Implementing == explicitly (can also be synthesized automatically)
    static func == (lhs: Point, rhs: Point) -> Bool {
        return lhs.x == rhs.x && lhs.y == rhs.y
    }
}

let p1 = Point(x: 1.0, y: 2.0)
let p2 = Point(x: 1.0, y: 2.0)
let p3 = Point(x: 3.0, y: 4.0)
print("p1 == p2: \(p1 == p2)")
print("p1 == p3: \(p1 == p3)")

// Comparable: ordering comparison
struct Student: Comparable {
    let name: String
    let score: Int

    // Only < needs to be implemented; <= / > / >= are synthesized automatically
    static func < (lhs: Student, rhs: Student) -> Bool {
        return lhs.score < rhs.score
    }
}

let students = [
    Student(name: "Alice", score: 85),
    Student(name: "Bob", score: 92),
    Student(name: "Carol", score: 78)
]

let sorted = students.sorted()
for s in sorted {
    print("\(s.name): \(s.score) points")
}

// Hashable: use as a key in Set or Dictionary
struct Color: Hashable {
    let r: Int, g: Int, b: Int
}

var colorSet: Set<Color> = [
    Color(r: 255, g: 0, b: 0),
    Color(r: 0, g: 255, b: 0),
    Color(r: 255, g: 0, b: 0)  // Duplicates are removed
]
print("Number of colors: \(colorSet.count)")

Notes

If all stored properties of a struct or enum already conform to Equatable or Hashable, the compiler can synthesize conformance automatically. You can omit implementations of == and hashValue.

For Comparable, you only need to implement <; the compiler generates the remaining operators (<=, >, >=) for you. Types conforming to Hashable must guarantee that if two values are equal (==), they have the same hashValue — this is the Hashable contract.

For the basics of protocols, see Protocol basics / Conformance.

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