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