Extensions in iOS

Jitendra Kumar

31 March 2021

Extensions in iOS provide help to add the new functionality of an existing class, structure, or enumeration type.

But overriding the functionality is not possible with extensions.

Extensions in iOS works the same as a category in objective-C.

So extension provides help for confirming the protocol.

Writing of extension is very simple and we can create an extension outside of class.

Extension syntax

extension type {
     // new fetaure code
}

extension type {

// new fetaure code

}

-> We can do the below things using the extensions.

A-> Add compute instance and type work properties.

B-> We can create the type and instance method.

C-> Extension provides the new initializer.

D-> We can define subscripts and nested features.

The extension can adopt more than one protocol.

extension SomeType: Protocol, Protocol {
    // implementation of protocol 
}

extension SomeType: Protocol, Protocol {

// implementation of protocol

}

Computed Type Property

The extension can add computed type and computed instance property.

we can create multiple functionalities then compute and get the results.

extension String { 
  var length: Int { 
   return self.count 
  } 
} 
print("webkul".count) 

output:- 6

extension String {

var length: Int {

return self.count

}

print("webkul".count)

output:- 6

so we can create a computed property from the above step.

=> Methods

We can create multiple methods in extensions according to our requirements with multiple types.

This will help us to use this method anywhere with the same datatype.

extension String {

   func getStringLength()-> int  {
      return self.count
  }

}

print("webkul".getStringLength())

output :- 6

extension String {

func getStringLength()-> int {

return self.count

}

print("webkul".getStringLength())

output :- 6

=> Initializer

Initializer use to provide the new and custom initialization of the existing type.

So This enables you to extend other types to accept your own custom types as initializer parameters.

struct intializerStruct {
    var width = 100.0
    var height = 200.0
}

//we can define the structure above and now we initialize through the extension 

extension intializerStruct {
 
   init(widthValue: Double, heightValue: Double) {
     self.width = widthValue
     self.height = heightValue
   }
}

now access the structure and print the width and height value

let obj = intializerStruct(widthValue: 400, heightValue: 500)

print("width", obj.width)

print("height", obj.height)

Output

width:-  400.0

height:- 500.0

struct intializerStruct {

var width = 100.0

var height = 200.0

}

//we can define the structure above and now we initialize through the extension

extension intializerStruct {

init(widthValue: Double, heightValue: Double) {

self.width = widthValue

self.height = heightValue

}

now access the structure and print the width and height value

let obj = intializerStruct(widthValue: 400, heightValue: 500)

print("width", obj.width)

print("height", obj.height)

Output

width:- 400.0

height:- 500.0

=> Subscripts

Extension provides a feature that adds a new subscript for an existing type.

This example provides us the string character according to the given index.

extension String {
    subscript(accessCharacterThroughIndex i: Int) -> Character {
        let index = self.index(startIndex, offsetBy: i)
        return self[index]
    }
}

let stringData = "webkul"

print("character on 0 index is:- ", stringData[accessCharacterThroughIndex: 0])

output

character on 0 index is:- w

extension String {

subscript(accessCharacterThroughIndex i: Int) -> Character {

let index = self.index(startIndex, offsetBy: i)

return self[index]

}

let stringData = "webkul"

print("character on 0 index is:- ", stringData[accessCharacterThroughIndex: 0])

output

character on 0 index is:- w

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