struct

類似於js object。

type Account struct {
    id      int
    name    int
}

必須大寫

上面範例在 json marshal 後無法解析

原因為 屬性第一個字必須大寫，struct名字第一個字也要大寫。

type Account struct {
    Id      int
    Name    int
}

初始化

如果只有一個欄位最後要加逗點

point := struct{ x, y int }{10, 20}
或是
point := new(Account)

更改值

point.x = 20
point.y = 30

傳值

package main

import "fmt"

type Point struct {
    X, Y int
}

func main() {
    point1 := Point{X: 10, Y: 20}
    point2 := point1

    point1.X = 20

    fmt.Println(point2) // {20, 20}
}

傳地址

如果是傳遞指，則會更改到參照的物件

package main

import "fmt"

type Point struct {
    X, Y int
}

func main() {
    point1 := Point{X: 10, Y: 20}
    point2 := &point1

    point1.X = 20

    fmt.Println(*point2) // {20, 20}
}

Struct inside Struct

type testS struct {
	cc int
}

type ss struct {
	testS
	ccc int
}

func main() {
	v := ss{testS: testS{cc: 22}, ccc: 1}
	fmt.Println(v)
}

推薦: https://ithelp.ithome.com.tw/articles/10227592

把func 加入到 struct內

有兩種方法：

第一種：

直接放入 struct

type ss struct {
	ccc      int
	getApple func()
}

func main() {
	v := ss{ccc: 1, getApple: func() {
		fmt.Println(22)
	}}
	fmt.Println(v)
}

第二種：

之後寫 func ，然後將 struct 放在 func 名稱前

https://go.dev/tour/methods/4

type Account struct {
    id      string
    name    string
    balance float64
}

func (ac *Account) Deposit(amount float64) {
    .....
}

account := &Account{"1234-5678", "Justin Lin", 1000}
account.Deposit(500)

例如原本要把參數傳進去才能呼叫 test ：

package main

import "fmt"

type connection struct {
	message chan string
}

var conn = connection{
	message: make(chan string),
}

func main() {
	go test(conn.message)

	msg := <-conn.message
	fmt.Println(msg)
}

func test(messages chan string) {
	messages <- "ping"
}

可以改為以下：讓test 變成 conn 的方法

package main

import "fmt"

type connection struct {
	message chan string
}

var conn = connection{
	message: make(chan string),
}


func (c *connection) test() {
	c.message <- "ping"
}


func main() {
	go conn.test()

	msg := <-conn.message
	fmt.Println(msg)
}

Value receiver, Pointer receiver

這邊要注意 connection 與 *connection 傳入時有分

https://matthung0807.blogspot.com/2021/06/go-value-receiver-pointer-receiver-difference.html

Func 傳值與傳址

type MyStruct struct {
    Val int
}

func myfunc() MyStruct {
    return MyStruct{Val: 1}
}

func myfunc() *MyStruct {
    return &MyStruct{}
}

func myfunc(s *MyStruct) {
    s.Val = 1
}

The first returns a copy of the struct, the second a pointer to the struct value created within the function, the third expects an existing struct to be passed in and overrides the value.

https://stackoverflow.com/questions/23542989/pointers-vs-values-in-parameters-and-return-values

iterate struct 內的值

package main

import (
	"fmt"
	"reflect"
)

type test struct {
	a int
	b int
}

func main() {

	vb := test{a: 12, b: 13}
	v := reflect.ValueOf(vb)
	for idx := 0; idx < v.NumField(); idx++ {
		keyNum := v.Field(idx)
		fmt.Println(keyNum)
	}
}

// 12
// 13

引入其他 package 的 struct

./user/schema.go

package user

type Schema struct {
	ID           int    `json:"id"`
	Name         string `json:"name"`
	Age          string `json:"age"`
	Account      string `json:"account"`
	Password     string `json:"password"`
	RegisterTime int64  `json:"registerTime"`
	Gender       string `json:"gender"`
	City         string `json:"city"`
}

main.go

import (
	USER "./user"
)

func main() {
	type User USER.Schema
	....
}	

Import struct from another package and file golangStack Overflow