如何将在函数内部创建的变量作为另一个函数的指针传递

Question

Hi Golang newbie here,

How to pass a variable as pointer argument to the another function.

func B(temp *?, event *Event) {
 temp["filla_a"] = event.Data["filla_a"]
 return temp
}

func A(event *Event) {
  temp := make(map[string]interface{})
  temp["po_id"] = event.Data["id"]
  temp = B(temp, event)
}

How to achive this in golang ?

Answer 1

This is how you can do it in go:

package main

import (
    "fmt"
)

type Event struct {
    Data map[string]string
}

func main() {
    e := new(Event)
    e.Data = make(map[string]string)
    e.Data["id"] = "THE_ID"
    e.Data["filla_a"] = "THE_FILLA_A"
    A(e)
}

func A(event *Event) {
    temp := make(map[string]interface{})
    temp["po_id"] = event.Data["id"]
    B(temp, event)
    fmt.Println(temp)
}

func B(temp map[string]interface{}, event *Event) map[string]interface{}{
    temp["filla_a"] = event.Data["filla_a"]
    return temp
}

I have assumed/made event as struct and declared the same in the program.

The map in go is a reference type (or better say it has pointer reference to internal data structures), so you do not need to pass a pointer of map, just pass/return the variable itself.

On the other hand struct (the Type of e in the main() function) is value type and need to be passed as a pointer to persist updates from called function.

NOTE: the new keyword creates a pointer to the type. Thus the variable e in the main() function is actually a pointer to the Type Event.

Go Playground: https://play.golang.org/p/Jbkm6z5a2Az

Hope it helps.