Swift Comparable Protocol

Before reading this post, I would suggest to go through my post on Equatable protocol

Because, Comparable protocol extends from Equatable Protocol.

Equatable helps in comparing custom class objects and finding them in a collection.

Comparable protocol helps in comparing(< , > , <=, >=) and sorting of custom class objects.

<= and >= uses Equatble stuff as Comparable protocol extends from to Equatable protocol.

Most of the native classes confirm to comparable protocol which gives direct comparison access.

       

 let fruit1 = "banana"

 let fruit2 = "grapes"

        

      if fruit1 < fruit2  {

         print("YES!")

      } 

      else {

         print("NO!")

      }

Most of the native classes confirm to comparable protocol which gives direct sort() method for collection.

       

 var fruits = ["banana", "apple", "grapes"]

 fruits.sort()

 print(fruits)  //["apple", "banana", "grapes"]

Here we don’t need to write any logic.

Where as for custom classes, We need to explicitly write the sort logic by using sort(by:) method.

       

  struct Address: Equatable {

    

    let city: String

    let state: String

    let country: String

    

   }

  var addresses = [

  Address(city: "Amsterdam", state: "New York", country: "America"),

  Address(city: "Belmont", state: "California", country: "America"),

  Address(city: "Hartford", state: "Connecticut", country: "America")]

        

 addresses.sort(by: { $0.state < $1.state })

Instead of this, Address struct can confirm to Comparable protocol and we can have ability to directly compare(< , > , <=, >=).

For Equatable, we don’t need to write boiler plate code from Swift 4.1 onwards, whereas for Comparable, we need to write.

       

 struct Address: Comparable {

    

      let city: String

      let state: String

      let country: String

    

      static func < (lhs: Address, rhs: Address) -> Bool {

          return lhs.city < rhs.city

      }

    

  }

I am comparing city name for sorting here.

Now, we can directly compare our Address custom objects with comparison operators(< , > , <=, >=).

       

    let currentAddress = Address(city: "Amsterdam", state: 
            "New York", country: "America")

    let selectedAddress = Address(city: "Hartford", state: 

            "Connecticut", country: "America")

        

        if currentAddress < selectedAddress {

            print("Show current address first")

        } 

        else {

            print("Show selectedAddress address first")

        }

As we are mentioned the logic for Comparison, Our Address collection will have direct sort() method now.

       

  var addresses = [

  Address(city: "Amsterdam", state: "New York", country:      
                                                                       "America"),

  Address(city: "Belmont", state: "California", country: 

                                                                       "America"),

  

  Address(city: "Hartford", state: "Connecticut", country:     

                                                                       "America")]

        

  addresses.sort()

That’s how we can make use of Comparable protocol and have comparison quite easy like native objects.

Hope this post is useful. Feel free to comment in case of any queries.