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TopicsFunction

🔹 1. What is a First-Class Function in Go?

Answer: In Go, functions are first-class citizens, meaning they:

  • Can be assigned to variables
  • Can be passed as arguments
  • Can be returned from other functions

✅ Example:

func greet(name string) string {
	return "Hello, " + name
}
 
var f = greet
 
fmt.Println(f("Go")) // Output: Hello, Go

🔹 2. What is a Higher-Order Function?

Answer: A Higher-Order Function is a function that:

  • Takes one or more functions as parameters
  • OR returns a function

✅ Example (passing function):

func operate(x int, y int, op func(int, int) int) int {
	return op(x, y)
}
 
func add(a, b int) int {
	return a + b
}
 
result := operate(5, 3, add) // 8

✅ Example (returning function):

func multiplier(factor int) func(int) int {
	return func(x int) int {
		return x * factor
	}
}
 
double := multiplier(2)
fmt.Println(double(5)) // Output: 10

🔹 3. What is an Anonymous Function in Go?

Answer: An anonymous function has no name. It’s often used for short, one-time behavior.

✅ Example:

func() {
	fmt.Println("Hello from anonymous function!")
}()

Or assigned to a variable:

square := func(x int) int {
	return x * x
}
fmt.Println(square(4)) // 16

🔹 4. What is an IIFE (Immediately Invoked Function Expression) in Go?

Answer: An IIFE is a function that is declared and immediately executed.

✅ Example:

result := func(a, b int) int {
	return a + b
}(10, 5)
 
fmt.Println(result) // Output: 15

This is useful for scoping or initializing inline values.

🔹 5. What is the Return Type in a Go Function?

Answer: In Go, functions must explicitly declare their return types. They can return:

  • A single value
  • Multiple values
  • Named or unnamed return variables

✅ Example (single return):

func square(x int) int {
	return x * x
}

✅ Example (multiple return):

func divide(a, b int) (int, error) {
	if b == 0 {
		return 0, fmt.Errorf("divide by zero")
	}
	return a / b, nil
}

✅ Example (named returns):

func sumAndProduct(x, y int) (sum int, product int) {
	sum = x + y
	product = x * y
	return
}

🔹 6. Can a Function Return Another Function in Go?

Answer: Yes. This is part of functional programming capability.

✅ Example:

func greeter(greeting string) func(string) string {
	return func(name string) string {
		return greeting + ", " + name
	}
}
 
sayHello := greeter("Hello")
fmt.Println(sayHello("John")) // Output: Hello, John

🔹 7. How to Pass a Function as an Argument?

Answer: Use the function type in the parameter list.

✅ Example:

func apply(x int, fn func(int) int) int {
	return fn(x)
}
 
fmt.Println(apply(5, func(n int) int { return n * 2 })) // Output: 10

🔹 8. Can Go Functions Be Recursive?

Answer: Yes, Go supports recursion.

✅ Example:

func factorial(n int) int {
	if n == 0 {
		return 1
	}
	return n * factorial(n-1)
}

🔹 9. What Are Variadic Functions?

Answer: A variadic function can accept a variable number of arguments.

✅ Example:

func sum(nums ...int) int {
	total := 0
	for _, n := range nums {
		total += n
	}
	return total
}
 
sum(1, 2, 3, 4) // Output: 10

🔹 10. Are Functions in Go Pure?

Answer: Functions in Go can be pure (no side effects), but Go does not enforce functional purity. It supports both functional and imperative styles.

🔹11. What is init function in go?

  • Special function that runs automatically before main()
  • Used for initial setup (e.g., config, variable initialization)
  • Runs once per file
  • A package can have multiple init() functions
  • Executed in file order within a package
  • Executed in import dependency order across packages
  • No parameters and no return values
  • ⚠️ Should be used only for minimal setup, not business logic
  • 🧪 Also runs before test functions in _test.go files
Error HandlingInterface