Extensions

Sunday, 30 September 2018

Extensions

Extensions means add additional functionality to existing types.
Extensions add new functionality to existing class, struct, enum or protocols.
Extensions are similar to categories in Objective-C.

Extension syntax
Declare Extension with "extension" keyword

extension Type {
    ///Additional functionality add hear

}

An Extension can extends one or more protocols.

extension Type : Protocol{
    ///protocols method hear
}

Example

extension String{
    ///Trim string value
    func toTrim() -> String{
        return self.trimmingCharacters(in: .whitespacesAndNewlines)
    }
}

///Simply use like below
let strName = " use of string extension "
print(strName)
print(strName.toTrim())

Output : 

 use of string extension 
use of string extension

Another example

extension UIView {
    func defaultRadius() {
        self.layer.cornerRadius = self.frame.size.width / 2
    }
}

let parentView = UIView.init(frame: CGRect.init(x: 0, y: 0, width: 50, height: 50))
parentView.backgroundColor = UIColor.red
parentView.defaultRadius()

Output: 

UIView Extension


Computed Properties

Extension can add computed instance property and computed type property to existing type.

Example

extension Int{
    var squareRoot : Int {
        return self * self
    }
}

let iValue = 5
print(iValue.squareRoot)

Output : 

25

Methods

Extensions add new instance method and type method to existence type.

Example

extension Int{
    func repeatValue(value : () -> Void) {
        for _ in 0..<self{
            value()
        }
    }
}

5.repeatValue {
    print("hello world")

}

Output :

hello world
hello world
hello world
hello world
hello world

For more about Extensions watch below video



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