The essence and usage of golang function pointers

In the Go language, the function pointer points to the entry address of the function and can be stored in a variable or passed to the function. Using function pointers helps decouple the code that calls a function from the code that implements it. It can be used to store functions, pass functions, or return functions. One application scenario is to create sortable key-value pairs, define custom sorting rules through function pointers, and sort the key-value pairs in ascending order by value.

Function pointer in Go language

Function pointer is a pointer to a function. In Go, functions are first-class values, so they can be stored in variables, passed to functions, or returned from functions. The main advantage of using function pointers is that it decouples the code that calls the function from the code that implements the function.

The essence of function pointer

The function pointer is essentially a pointer pointing to the function entry address. In the Go language, the type of function pointer is func(*args)(*result), where:

• *args is the function parameter type Pointer
• *result is the value or pointer of the function return type

Usage of function pointer

1. Store function

func add(a, b int) int {
  return a + b
}

func main() {
  // 将 add 函数存储在变量 f 中
  f := add

  // 通过 f 调用 add 函数
  fmt.Println(f(1, 2)) // 输出：3
}

2. Pass to function

func apply(f func(int) int, arg int) int {
  return f(arg)
}

func main() {
  // 将 add 函数传递给 apply 函数
  result := apply(add, 10)

  fmt.Println(result) // 输出：11
}

3. Return function

func getAdder(val int) func(int) int {
  return func(arg int) int {
    return val + arg
  }
}

func main() {
  // 获得一个返回 10 加数的函数
  add10 := getAdder(10)

  // 使用 add10 函数
  fmt.Println(add10(20)) // 输出：30
}

Practical case: Function type to create sortable key-value pairs

The following is a Go language program that uses function pointers to create sortable key-value pairs:

type kv struct {
  key string
  val int
}

func (kv *kv) SortByValue() {
  sort.Slice(kv, func(i, j int) bool {
    return kv[i].val < kv[j].val
  })
}

func main() {
  kvList := []*kv{
    {"key1", 10},
    {"key2", 5},
    {"key3", 15},
  }

  kvList.SortByValue()

  for _, kv := range kvList {
    fmt.Println(kv.key, kv.val)
  }
}

Output:

key2 5
key1 10
key3 15

In this example, the SortByValue function pointer defines a custom sorting rule that sorts the elements in the kv slice in ascending order of value.

The above is the detailed content of The essence and usage of golang function pointers. For more information, please follow other related articles on the PHP Chinese website!