Golang study notes-function as value use

Concept

在C和C++中，函数是一组指令的集合，这组指令的入口地址用函数名来表示，所以，在C和C++中，函数名称是一个地址。  

In the go language, however, a function is a type and is the first type (first-class). His status is the same as the type int string.
We often declare a variable of value type int or string, and now we can declare a variable with a value type of a function called a function variable that is, the function can be assigned as a value type to the variable

Example:

func Add(a,b int)int{    return a+b}func simple01(){    //声明一个int类型的变量    var number = 3    fmt.Println(number)    //声明一个string类型的变量    str:="aabbcc"    fmt.Println(str)    //现在我们声明一个函数类型的变量    myFunc:=Add    //通过函数变量调用函数(用函数指针来理解，还是很容易的)    fmt.Println(myFunc(1,2))}

Execution Result:

3
Aabbcc
3

Use of function variables

In the

most basic usage, a function variable is passed directly as a value, such as: an argument passed into a function can pass in a function variable
Another way to use, the most common method, is to use the TYEP keyword to define a custom class type with the underlying type as the function type. When a function is assigned to such a variable as a value, the signature of the function must be the same (parameter and return value of the function)

Example:

type ProcessBasename func(string)string//basename函数 移除字符串的路径部分和.后缀 只取文件名func basename(str string)string{    //去除路径部分    slash:=strings.LastIndex(str,"/") //如果没有找到"/" LastIndex返回-1    str=str[slash+1:]    //取出.的前一部分    if dot:=strings.LastIndex(str,".");dot>0{        str = str[:dot]    }    return str}//这个函数使用了函数变量作为参数func GetBaseName(str string,myBasenameFunc func(string)string)string{    return myBasenameFunc(str)}//这个函数使用了type关键字自定义的类型(底层是一种函数类型)func GetBaseName1(str string,processBasename ProcessBasename)string{    return processBasename(str)}//函数变量被当做函数参数传递func simple02(){    str:="a/b/c.go"    //将函数basename作为实参传递给GetBaseName    //要注意，函数变量basename的函数签名要和形参myBasenameFunc的函数签名完全一致    //在这里，函数签名是指 函数的参数和返回值    fmt.Println(GetBaseName(str,basename))    str1:="c.d.go"    fmt.Println(GetBaseName1(str1,basename))}

Execution Result:

C
C.D

Summarize

the steps and meanings of using function variables

    1.定义一个底层为函数类型的自定义类型      2.实现定义的函数类型      3.作为参数调用  

using a function variable allows the program to execute logic based on the actual function passed by the user, where the function type is called. Makes the program more flexible

Example: In the program according to the actual function passed by the user to achieve two numbers plus or minus

type CalculateFunc func(a,b int)intfunc Add(a,b int)int{    return a+b}func Sub(a,b int)int{    return a-b}func Calculate(a,b int,calculateFunc CalculateFunc)int{    return calculateFunc(a,b)}func simple03(){    a,b:=5,3    //相加    add:=Calculate(a,b,Add)    //相减    sub:=Calculate(a,b,Sub)    println(add,sub)}func main(){    simple01()    simple02()    simple03()}

Execution Result:

8 2