Equatable Interface

🚧 Status: The Equatable interface is not implemented yet.

An equatable type is a type that can be compared for equality. Types are equatable when they implement the Equatable interface.

Equatable types can be compared for equality using the equals operator (==) or inequality using the unequals operator (!=).

Most of the built-in types are equatable, like booleans and integers. Arrays are equatable when their elements are equatable. Dictionaries are equatable when their values are equatable.

To make a type equatable the Equatable interface must be implemented, which requires the implementation of the function equals, which accepts another value that the given value should be compared for equality.

struct interface Equatable {
    pub fun equals(_ other: {Equatable}): Bool
}

// Declare a struct named `Cat`, which has one field named `id`
// that has type `Int`, i.e., the identifier of the cat.
//
// `Cat` also will implement the interface `Equatable`
// to allow cats to be compared for equality.
//
struct Cat: Equatable {
    pub let id: Int

    init(id: Int) {
        self.id = id
    }

    pub fun equals(_ other: {Equatable}): Bool {
        if let otherCat = other as? Cat {
            // Cats are equal if their identifier matches.
            //
            return otherCat.id == self.id
        } else {
            return false
        }
    }
}

Cat(1) == Cat(2)  // is `false`
Cat(3) == Cat(3)  // is `true`