Swift - Methods



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In Swift 4 language Functions associated with particular types are referred to as Methods. In Objective C Classes are used to define methods, whereas Swift 4 language provides the user flexibility to have methods for Classes, Structures and Enumerations.

Instance Methods

In Swift 4 language, Classes, Structures and Enumeration instances are accessed through the instance methods.

Instance methods provide functionality

  • To access and modify instance properties
  • functionality related to the instance's need

Instance method can be written inside the {} curly braces. It has implicit access to methods and properties of the type instance. When a specific instance of the type is called it will get access to that particular instance.

Syntax

func funcname(Parameters) -> returntype {
   Statement1
   Statement2
   ---
   Statement N
   return parameters
}

Example

Live Demo
class calculations {
   let a: Int
   let b: Int
   let res: Int

   init(a: Int, b: Int) {
      self.a = a
      self.b = b
      res = a + b
   }
   
   func tot(c: Int) -> Int {
      return res - c
   }
   
   func result() {
      print("Result is: \(tot(c: 20))")
      print("Result is: \(tot(c: 50))")
   }
}
let pri = calculations(a: 600, b: 300)
pri.result()

When we run the above program using playground, we get the following result −

Result is: 880
Result is: 850

Class Calculations defines two instance methods −

  • init() is defined to add two numbers a and b and store it in result 'res'
  • tot() is used to subtract the 'res' from passing 'c' value

Finally, to print the calculations methods with values for a and b is called. Instance methods are accessed with '.' dot syntax

Local and External Parameter Names

Swift 4 Functions describe both local and global declarations for their variables. Similarly, Swift 4 Methods naming conventions also resembles as that of Objective C. But the characteristics of local and global parameter name declarations are different for functions and methods. The first parameter in Swift 4 are referred by preposition names as 'with', 'for' and 'by' for easy to access naming conventions.

Swift 4 provides the flexibility in methods by declaring first parameter name as local parameter names and the remaining parameter names to be of global parameter names. Here 'no1' is declared by Swift 4 methods as local parameter names. 'no2' is used for global declarations and accessed through out the program.

Live Demo
class division {
   var count: Int = 0
   func incrementBy(no1: Int, no2: Int) {
      count = no1 / no2
      print(count)
   }
}

let counter = division()
counter.incrementBy(no1: 1800, no2: 3)
counter.incrementBy(no1: 1600, no2: 5)
counter.incrementBy(no1: 11000, no2: 3)

When we run the above program using playground, we get the following result −

600
320
3666

External Parameter Name with # and _ Symbol

Even though Swift 4 methods provide first parameter names for local declarations, the user has the provision to modify the parameter names from local to global declarations. This can be done by prefixing '#' symbol with the first parameter name. By doing so, the first parameter can be accessed globally throughout the modules.

When the user needs to access the subsequent parameter names with an external name, the methods name is overridden with the help of '_' symbol.

Live Demo
class multiplication {
   var count: Int = 0
   func incrementBy(no1: Int, no2: Int) {
      count = no1 * no2
      print(count)
   }
}

let counter = multiplication()

counter.incrementBy(no1: 800, no2: 3)
counter.incrementBy(no1: 100, no2: 5)
counter.incrementBy(no1: 15000, no2: 3)

When we run the above program using playground, we get the following result −

2400
500
45000

Self property in Methods

Methods have an implicit property known as 'self' for all its defined type instances. 'Self' property is used to refer the current instances for its defined methods.

Live Demo
class calculations {
   let a: Int
   let b: Int
   let res: Int

   init(a: Int, b: Int) {
      self.a = a
      self.b = b
      res = a + b
      print("Inside Self Block: \(res)")
   }
   
   func tot(c: Int) -> Int {
      return res - c
   }
   
   func result() {
      print("Result is: \(tot(c: 20))")
      print("Result is: \(tot(c: 50))")
   }
}

let pri = calculations(a: 600, b: 300)
let sum = calculations(a: 1200, b: 300)

pri.result()
sum.result()

When we run the above program using playground, we get the following result −

Inside Self Block: 900
Inside Self Block: 1500
Result is: 880
Result is: 850
Result is: 1480
Result is: 1450

Modifying Value Types from Instance Methods

In Swift 4 language structures and enumerations belong to value types which cannot be altered by its instance methods. However, Swift 4 language provides flexibility to modify the value types by 'mutating' behavior. Mutate will make any changes in the instance methods and will return back to the original form after the execution of the method. Also, by the 'self' property new instance is created for its implicit function and will replace the existing method after its execution

Live Demo
struct area {
   var length = 1
   var breadth = 1
   
   func area() -> Int {
      return length * breadth
   }
   mutating func scaleBy(res: Int) {
      length *= res
      breadth *= res
      print(length)
      print(breadth)
   }
}

var val = area(length: 3, breadth: 5)
val.scaleBy(res: 3)
val.scaleBy(res: 30)
val.scaleBy(res: 300)

When we run the above program using playground, we get the following result −

9
15
270
450
81000
135000

Self Property for Mutating Method

Mutating methods combined with 'self' property assigns a new instance to the defined method.

Live Demo
struct area {
   var length = 1
   var breadth = 1
   func area() -> Int {
      return length * breadth
   }
   mutating func scaleBy(res: Int) {
      self.length *= res
      self.breadth *= res
      print(length)
      print(breadth)
   }
}

var val = area(length: 3, breadth: 5)
val.scaleBy(res: 13)

When we run the above program using playground, we get the following result. −

39
65

Type Methods

When a particular instance of a method is called, it is called as an Instance method; and when the method calls a particular type of a method, it is called as 'Type Methods'. Type methods for 'classes' are defined by the 'func' keyword and structures and enumerations type methods are defined with the 'static' keyword before the 'func' keyword.

Type methods are called and accessed by '.' syntax where instead of calling a particular instance the whole method is invoked.

Live Demo
class Math {
   class func abs(number: Int) -> Int {
      if number < 0 {
         return (-number)
      } else {
         return number
      }
   }
}

struct absno {
   static func abs(number: Int) -> Int {
      if number < 0 {
         return (-number)
      } else {
         return number
      }
   }
}

let no = Math.abs(number: -35)
let num = absno.abs(number: -5)

print(no)
print(num)

When we run the above program using playground, we get the following result. −

35
5


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