Golang function pointers and closures: concept analysis

Summary: 1. What is a function pointer? A function pointer is a variable that stores the address of a function, allowing a function to be passed as a parameter to another function. 2. What is closure? A closure is a function that appends data to a function. It captures the scope variables when the function is called, allowing the function to refer to external variables even if they have been released from the scope.

Golang function pointers and closures: Concept analysis

Function pointers

A function pointer is a variable that stores the address of a function. It allows passing a function as an argument to another function. The syntax is as follows:

type FuncType func(params) (return type)
var functionPointer FuncType
functionPointer = func(params) (return type) { ... }

Closure

A closure is a function that appends additional data to a function. It captures the scope variables when the function is called. This allows functions to reference external variables even if they have been released by their scope.

Syntax:

func enclosingFunction(params) (return type) {
    // 外部变量声明
    
    // 内部函数（闭包）
    innerFunction := func(innerParams) (return type) {
        // 内部函数可以访问外部变量
        
        // 返回值
    }
    
    // 返回内部函数（闭包）
    return innerFunction
}

Practical case: Sorting

Suppose we have a []int Array, we want to sort it in ascending or descending order. We can use Golang's sort package, which provides a Sort function that takes a comparison function as a parameter.

The following is an example of using closures to create a custom comparison function:

package main

import (
    "sort"
)

// 定义排序方式
type SortOrder string

const (
    Ascending SortOrder = "ASC"
    Descending SortOrder = "DESC"
)

// 根据指定顺序创建比较函数
func createComparator(sortOrder SortOrder) func(a, b int) bool {
    return func(a, b int) bool {
        if sortOrder == Ascending {
            return a < b
        }
        return a > b
    }
}

func main() {
    numbers := []int{3, 5, 2, 1, 4}
    
    // 使用升序比较函数排序
    sort.Slice(numbers, createComparator(Ascending))
    
    // 使用降序比较函数排序
    sort.Slice(numbers, createComparator(Descending))
}

In this example:

• createComparator The function accepts Takes a SortOrder as argument and returns a comparison function.
• The comparison function is a closure that captures the sortOrder variable even if the createComparator function has returned.
• The comparison function compares two numbers in order according to sortOrder using Ascending or Descending. The
• main function demonstrates how to sort an array in ascending and descending order using a custom comparison function.

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