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Swift's Generics Enhancing Code Flexibility and Reusability

By David Li on 2023-11-16T13:30:07.000Z

Swift’s Generics: Enhancing Code Flexibility and Reusability

Generics are a powerful feature in the Swift programming language that enables developers to write flexible and reusable code with less duplication. In this article, we will discuss what generics are, why they are important, and how to use them in your Swift code.

What are Generics?

Generics are a programming language feature that allows you to write a single function or class that can work with different types, without specifying the type in advance. The type is supplied as a parameter when the function or class is used, allowing for a more reusable and type-safe code.

In Swift, generics are used extensively in the standard library, particularly for collection types such as Array, Dictionary, and Set. These collection types can store elements of any type, allowing for a high level of flexibility and adaptability.

Why Use Generics?

Generics provide several benefits to developers, including:

  1. Code reusability: Generics allow you to write a single function or class that works with multiple types, reducing the need for writing separate implementations for each type.
  2. Type safety: When working with generics, the Swift compiler enforces strict type-checking, ensuring that your code remains type-safe and less prone to runtime errors.
  3. Performance: Generics are implemented during compilation, which means that the performance impact is minimal, and in many cases, the generated code is just as efficient as if you had written specific, non-generic implementations.

How to Use Generics in Swift

To use generics in Swift, you need to define a generic function, class, or structure. Let’s explore how to do this through examples.

Generic Functions

To define a generic function, use angle brackets <T> after the function name, where T is a placeholder for the type that will be supplied later. Here’s an example of a simple generic function that swaps the values of two variables:

func swapValues<T>(a: inout T, b: inout T) {
    let temporaryA = a
    a = b
    b = temporaryA

var number1 = 5
var number2 = 10
swapValues(a: &number1, b: &number2)
print("number1: \(number1), number2: \(number2)") // Output: number1: 10, number2: 5

In this example, T is a type placeholder that can be replaced with any type when the function is called. The Swift compiler will infer the type based on the function call’s arguments.

Generic Types

You can also define generic classes, structures, and enumerations. Let’s illustrate this with a generic Stack class:

struct Stack<Element> {
    private var elements: [Element] = []

    mutating func push(_ element: Element) {

    mutating func pop() -> Element? {
        return elements.popLast()

    func peek() -> Element? {
        return elements.last

var intStack = Stack<Int>()
print(intStack.pop()) // Output: Optional(2)

var stringStack = Stack<String>()
print(stringStack.pop()) // Output: Optional("World")

In this example, the Stack structure uses a type placeholder Element to represent the type of elements it stores. When creating a new Stack instance, you need to specify the type of elements it will store.

Type Constraints

Sometimes, it’s necessary to constrain the types that can be used with a generic function or type. You can use type constraints to restrict the types that can be used as a placeholder. Here’s an example of a generic function that calculates the sum of two Numeric values:

func sum<T: Numeric>(a: T, b: T) -> T {
    return a + b

print(sum(a: 5, b: 10)) // Output: 15
print(sum(a: 3.14, b: 2.71)) // Output: 5.85
// Error: Cannot invoke 'sum' with an argument list of type '(a: String, b: String)'
// print(sum(a: "Hello", b: "World"))

In this example, we use the Numeric protocol as a type constraint to ensure that the function only accepts numeric types. The Swift compiler will enforce this constraint and generate an error if a non-numeric type is used.


Generics are a powerful feature in Swift that enable you to write flexible, reusable, and type-safe code. They play a vital role in the standard library and can significantly improve your code’s maintainability and performance. By understanding and utilizing generics in your Swift code, you can create more versatile and efficient codebases.

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