Swift - Type Aliases

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Swift provides a special feature named Type Aliases. Type aliases are used to define another name or aliases for the pre-defined types. It only gives a new name to the existing type and does not create a new type. For example, "Int" can also be defined as "myInt".

After defining type alias, we can use that alias anywhere in the program. A single program can contain more than one alias. A type alias is commonly used to improve code readability, code quality and abstracting complex types. We can define type aliases with the help of the type alias keyword.

Syntax

Following is the syntax of the type alias –

typealiase newName = existingType

We can define type aliases for the following data types −

• Primitive Data Types

• User Defined Data Types

• Complex Data Types

Type Aliases for Primitive Data Types in Swift

Primitive data types are the pre-defined data types provided by Swift such as Int, Float, Double, Character and String. With the help of a type alias, we can provide a new name to the in-built data types which can be used throughout the program without any error. For example, "typealias myString = String" now using myString we can create a string type variable.

Syntax

Following is the syntax of the type alias for primitive data types −

typealias newName = PreDefinedDataType

Here the PreDefinedDataType can be Int, Float, Double, String and Character.

Example

Swift program to create a type alias for in-built data types.

import Foundation

// Creating type typealias for String
typealias myString = String

// Creating type typealias for Float
typealias myNum = Float

// Creating type typealias for Int
typealias Num = Int

// Declaring integer type variable using Num
var number : Num = 10

// Declaring string type variable using myString
var newString : myString = "Tutorialspoint"

// Declaring float type variable using myNum
var value : myNum = 23.456

print("Number:", number)
print("type:", type(of: number))

print("\nString:", newString)
print("type:", type(of: newString))

print("\nFloat:", value)
print("type:", type(of: value))

Output

Number: 10
type: Int

String: Tutorialspoint
type: String
Float: 23.456
type: Float

Type Aliases for User- Defined Data Types in Swift

Using type aliases, we can also provide an alternate name to the user-defined data types. For example, "typealias mySet = Set<String>" now using mySet we can create a set of string type.

Syntax

Following is the syntax of the type alias for user-defined data types −

typealias newName = dataType

Here the datatype can be Array, Set, dictionary, etc.

Example

Swift program to create a type alias for user-defined data types.

import Foundation

// Creating type typealias for Set
typealias mySet = Set<Int>

// Creating type typealias for Array
typealias myNum = Array<Int>

// Creating type typealias for Array
typealias Num = Array<String>

// Declaring set of integer type using mySet
var newSet : mySet = [32, 3, 1, 2]

// Declaring array of integer type using myNum
var newArray : myNum = [32, 2, 1, 1, 3]

// Declaring array of string type using Num
var newArr : Num = ["Swift", "C++", "C#"]

print("Set:", newSet)
print("Array:", newArray)
print("Array:", newArr)

Output

Set: [32, 3, 1, 2]
Array: [32, 2, 1, 1, 3]
Array: ["Swift", "C++", "C#"]

Type Aliases for Complex Data Types in Swift

Complex data are the special type of data types which contain more than one pre-defined data type. So using types aliases we can also create aliases of complex data types. For example, (String, String) -> string as "MyString".

Syntax

Following is the syntax of type aliases for complex data types −

typealias newName = CdataType

Here the CdataType can be any complex data type like (String)->(String).

Example

Swift program to create a type alias for complex data types.

import Foundation

// Creating type typealias for function type
typealias Value = (String, String) -> String

func addStr(s1: String, s2: String) -> String{
   return s1 + s2
}
// Assigning addStr function to Value
var newFunc : Value = addStr

// Calling function
var result = newFunc("Hello", "World")

print(result)

Output

HelloWorld