Higher-Order Functions (Passing a Function as an Argument)

In this lesson you will learn how to pass a function as an argument in Go, so you can treat behaviour itself as a reusable part. This is for anyone searching for "Go higher-order functions how to use".

Passing another function as an argument is what makes something a higher-order function. Picture handing over the rules for a job and letting someone else do the work. Giving a comparison rule to sort.Slice is the classic example.

The sample code sorts in descending order by passing the ordering criterion as an anonymous function, as in sort.Slice(nums, func(i, j int) bool { return nums[i] > nums[j] }). It is a mechanism that shows off how freely Go treats functions as values.

A common stumbling block for beginners is what the comparison function's return value means. Returning true means "put i before j", so the way you write the condition is what decides ascending or descending order.

In real-world development the same idea applies to designs that swap behaviour by situation, and it is exactly how library functions such as sort.Slice are designed.

📖 Reference code

package main

import (
    "fmt"
    "sort"
)

func main() {
    nums := []int{5, 2, 8, 1}
    sort.Slice(nums, func(i, j int) bool {
        return nums[i] > nums[j]
    })
    fmt.Println(nums)
}

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