How can a function be passed as an argument to be called inside another function?

In Go, functions are first-class citizens, so they can be passed as arguments to other functions.

Example of passing a function to another function:

package main

import "fmt"

// Function that takes another function as an argument
func applyOperation(a, b int, op func(int, int) int) int {
    return op(a, b)
}

func main() {
    sum := func(x, y int) int {
        return x + y
    }

    result := applyOperation(3, 4, sum)
    fmt.Println(result) // Outputs 7
}

Here, applyOperation takes two numbers and a function op that defines the operation on these numbers. In main, we pass an anonymous addition function.

Thus, to pass a function in Go, it is enough to specify the argument type as func(...) ... and pass the desired function when calling.