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In the previous exercise, we saw how to create our own protocols. The Swift standard library includes many useful protocols that you can have your structures, classes, or enums conform to. A useful example is Hashable.

The Hashable protocol is used to make structs, classes, and enums able to be added to Sets and Dictionaries. To conform to Hashable, a struct, class, or enum either needs to have a hashValue property or to have only properties that already conform to Hashable. Most basic Swift types conform to Hashable. The following code won’t compile:

struct Resident {
    var name: String
    var age: Int
    var address: String
    var socialSecurityNum: String
}

let taxesByResident = [Resident: Double]() // ERROR: Type 'Resident' does not conform to protocol 'Hashable'

We can make this code compile by adding the Hashable protocol to Resident:

struct Resident: Hashable {
    let name: String
    let age: Int
    let address: String
    let socialSecurityNum: String
}

let taxesByResident = [Resident: Double]()

Hashable is just one of many protocols in Swift! For more on common protocols, check out the link here to Apple’s documentation.

Instructions

Create a struct Store that has a name of type String and a products property of type [String].

Create a constant of type Store named jaysPizza and assign it to a store with a name of “Jay’s Pizza” and products ["Pizza", "Soda", "Salad"].

Create a property named salesByStore of type [Store: Double] using type annotation, and assign it to a dictionary that maps jaysPizza to 100. You should get a compiler error!

Make the Store conform to Hashable. The code should now compile!

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