Understand the usage of functions and methods in go language

Catalog

Function definition syntax

Function definition example

No return function

Single return function

Multiple return function

Method (Method) Definition

Method (Method) Example

Basic types

Type of structure

Function definition syntax

Consistent with most languages ,Go The function definition in language is basically consistent with that in other languages

func function_name(Parameter-list) { // function body...}func function_name(Parameter-list) Return-Type { // function body...}func function_name(Parameter-list) (Multiple Return-Types){ // function body..}

func: Function definition keywords

function_name: The name of the function ,Go Language is mainly used camel-case( hump ) Way of naming , Also according to the nature of the function , Use initial case to distinguish functions , The details will be explained in the later special chapters Go The norms of language

Parameter-list: parameter list , If nothing can be ignored

Return-Type/Multiple Return-Types: Type of return value , namely return Type of return value , Here, three forms are distinguished ：

No return value / Single return value / Multiple return values

The other two are slightly different in the use of parentheses , Single return types generally do not add parentheses , For multiple return values, you need to add parentheses

In addition, for the sake of beauty , Parentheses after the parameter list , There is a space between the suggestion and the return type

Function definition example No return function func HelloFunc() { fmt.Println("Hello, World")} Single return function

This example demonstrates the parameter definition method and the return value type definition method

func HelloFunc(msg string) string { return "Hello, " + msg} Multiple return function

The type of the second return value is usually used to return an error , This is convenient for the program to handle exceptions

func HelloFunc(msg string) (string, error) { return "Hello, " + msg, nil}

Let's take a look at the complete code implementation , Call in main function HelloFunc when , You also need two variables to receive the corresponding values

package mainimport "fmt"func HelloFunc(msg string) (string, error) { return "Hello, " + msg, nil}func main() { printString, err := HelloFunc("World") if err == nil { fmt.Println(printString) }} Method (Method) Definition

Go There are no classes in language , So in Go Language provides a method definition similar to function definition , By adding Reciever type , Implement the definition of a method in a similar class , Methods can be used Reciver Properties of . Let's take a look at grammar ：

func (Reciever-Name Type) function_name(Parameter-list) (Multiple Return-Types){ // function body..}

Because most definitions are the same as the above function definitions , No more details here , Just introduce the new part ：

Reciever-Name： The type must be a custom type , Cannot be built-in int, string etc. , Use the words , Errors will be reported at compile time

Method (Method) Example Basic types

Let's look at a method implemented by basic types , Here we use a knowledge point that we haven't learned —— Custom type type, It will be explained in detail later , Don't tangle here . The meaning of this sentence is through custom types mystring Redefined variables , Essentially with string The same type .

type mystring string

Notice our function definition here , Before the function name , More (msg mystring) The definition of , And inside the function , We can also use msg

func (msg mystring) HelloFunc() { str := "Hello, " + msg fmt.Println(str)}

And in the main When calling in a function , Different from the function call above , We use call directly mymsg Methods HelloFunc, It implements a method similar to the above example

var mymsg mystringmymsg = "World"mymsg.HelloFunc()

The full code is shown below

package mainimport "fmt"type mystring stringfunc (msg mystring) HelloFunc() { str := "Hello, " + msg fmt.Println(str)}func main() { var mymsg mystring mymsg = "World" mymsg.HelloFunc()} Type of structure

In fact, from the source code of each project , Methods are more related to structures (struct) And interface (interface) Use it together , These will be explained in detail later , All you need to know is . Here is a simple example , Let's calculate the area of the rectangle .

Defines a structure rect, It contains two attributes: length and width

How to calculate the area area(),Reciver Defined as structure type , In this way, the body , You can use length and width to calculate the area

Main function , Defines a structure , And the initialization length and width are 3 and 4

Call the r.area() Complete the area calculation

package mainimport "fmt"type rect struct { width float64 height float64}func (r rect) area() float64 { return r.width * r.height}func main() { r := rect{3, 4} rectArea := r.area() fmt.Printf("Rect area is %v\n", rectArea)}

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