Generic function declaration in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a generic swap function

What is the output of this Swift code that uses a generic function to swap two values?

Swift

func swapValues<T>(_ a: inout T, _ b: inout T) {
    let temp = a
    a = b
    b = temp
}

var x = 5
var y = 10
swapValues(&x, &y)
print("x = \(x), y = \(y)")

A Compilation error due to generic function

B x = 5, y = 10

C x = 0, y = 0

D x = 10, y = 5

💡 Hint

Think about what the swap function does to the values passed by reference.

The generic function swaps the values of x and y by using inout parameters. After calling swapValues, x becomes 10 and y becomes 5.

❓ Predict Output

intermediate

Output of generic function with different types

What is the output of this Swift code using a generic function that prints the type and value?

Swift

func printValue<T>(_ value: T) {
    print("Value: \(value), Type: \(type(of: value))")
}

printValue(42)
printValue("Hello")

A Value: 42, Type: String\nValue: Hello, Type: Int

B Value: 42, Type: Int\nValue: Hello, Type: String

C Value: 42, Type: Optional<Int>\nValue: Hello, Type: Optional<String>

D Compilation error due to type mismatch

💡 Hint

The generic function accepts any type and prints its value and type.

The generic function printValue prints the value and its actual type. 42 is Int and "Hello" is String.

❓ Predict Output

advanced

Output of generic function with constraints

What is the output of this Swift code using a generic function constrained to Comparable?

Swift

func findMax<T: Comparable>(_ a: T, _ b: T) -> T {
    return a > b ? a : b
}

print(findMax(3, 7))
print(findMax("apple", "banana"))

A Compilation error due to missing Comparable conformance

B 3\napple

C 7\nbanana

D Runtime error due to type mismatch

💡 Hint

The function returns the greater of two Comparable values.

The function findMax returns the larger value between a and b. 7 is greater than 3, and "banana" is lexicographically greater than "apple".

🔧 Debug

advanced

Identify the error in this generic function declaration

What error does this Swift code produce when compiling?

Swift

func printFirstElement<T>(array: [T]) -> T {
    return array[0]
}

print(printFirstElement(array: []))

A Runtime error: Index out of range

B Compilation error: Missing return statement

C Compilation error: Generic type T not specified

D No error, prints nil

💡 Hint

Consider what happens when accessing the first element of an empty array.

The function tries to return the first element of an empty array, causing a runtime crash due to index out of range.

🧠 Conceptual

expert

Understanding generic function type inference

Given the generic function below, what is the inferred type of T when calling foo(5) and foo("test") respectively?

Swift

func foo<T>(_ value: T) -> String {
    return "Value is \(value)"
}

// Calls:
// foo(5)
// foo("test")

A T is Int for foo(5) and String for foo("test")

B T is always Any for all inputs

C T is always String regardless of input

D Compilation error due to ambiguous type inference

💡 Hint

Generic functions infer T based on the argument type at each call.

The compiler infers T as Int when foo(5) is called and as String when foo("test") is called, allowing the function to work with different types.