A type that provides an integer hash value.


You can use any type that conforms to the Hashable protocol in a set or as a dictionary key. Many types in the standard library conform to Hashable: Strings, integers, floating-point and Boolean values, and even sets provide a hash value by default. Your own custom types can be hashable as well. When you define an enumeration without associated values, it gains Hashable conformance automatically, and you can add Hashable conformance to your other custom types by adding a single hashValue property.

A hash value, provided by a type’s hashValue property, is an integer that is the same for any two instances that compare equally. That is, for two instances a and b of the same type, if a == b, then a.hashValue == b.hashValue. The reverse is not true: Two instances with equal hash values are not necessarily equal to each other.

Conforming to the Hashable Protocol

To use your own custom type in a set or as the key type of a dictionary, add Hashable conformance to your type. The Hashable protocol inherits from the Equatable protocol, so you must also satisfy that protocol’s requirements.

A custom type’s Hashable and Equatable requirements are automatically synthesized by the compiler when you declare Hashable conformance in the type’s original declaration and your type meets these criteria:

  • For a struct, all its stored properties must conform to Hashable.

  • For an enum, all its associated values must conform to Hashable. (An enum without associated values has Hashable conformance even without the declaration.)

To customize your type’s Hashable conformance, to adopt Hashable in a type that doesn’t meet the criteria listed above, or to extend an existing type to conform to Hashable, implement the hashValue property in your custom type. To ensure that your type meets the semantic requirements of the Hashable and Equatable protocols, it’s a good idea to also customize your type’s Equatable conformance to match.

As an example, consider a GridPoint type that describes a location in a grid of buttons. Here’s the initial declaration of the GridPoint type:

/// A point in an x-y coordinate system.
struct GridPoint {
    var x: Int
    var y: Int

You’d like to create a set of the grid points where a user has already tapped. Because the GridPoint type is not hashable yet, it can’t be used as the Element type for a set. To add Hashable conformance, provide an == operator function and a hashValue property.

extension GridPoint: Hashable {
    var hashValue: Int {
        return x.hashValue ^ y.hashValue &* 16777619

    static func == (lhs: GridPoint, rhs: GridPoint) -> Bool {
        return lhs.x == rhs.x && lhs.y == rhs.y

The hashValue property in this example combines the hash value of a grid point’s x property with the hash value of its y property multiplied by a prime constant.

Now that GridPoint conforms to the Hashable protocol, you can create a set of previously tapped grid points.

var tappedPoints: Set = [GridPoint(x: 2, y: 3), GridPoint(x: 4, y: 1)]
let nextTap = GridPoint(x: 0, y: 1)
if tappedPoints.contains(nextTap) {
    print("Already tapped at (\(nextTap.x), \(nextTap.y)).")
} else {
    print("New tap detected at (\(nextTap.x), \(nextTap.y)).")
// Prints "New tap detected at (0, 1).")


Providing a Hash Value

var hashValue: Int

The hash value.

Required. Default implementation provided.


Inherits From

Adopted By