Call a function from another package in Go

I have two files main.go which is under package main, and another file with some functions in the package called functions.

My question is: How can I call a function from package main?

File 1: main.go (located in MyProj/main.go)

package main


import "fmt"
import "functions" // I dont have problem creating the reference here


func main(){
c:= functions.getValue() // <---- this is I want to do
}

File 2: functions.go (located in MyProj/functions/functions.go)

package functions


func getValue() string{
return "Hello from this another package"
}
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最佳答案

You import the package by its import path, and reference all its exported symbols (those starting with a capital letter) through the package name, like so:

import "MyProj/functions"


functions.GetValue()
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  • You should prefix your import in main.go with: MyProj, because, the directory the code resides in is a package name by default in Go whether you're calling it main or not. It will be named as MyProj.

  • package main just denotes that this file has an executable command which contains func main(). Then, you can run this code as: go run main.go. See here for more info.

  • You should rename your func getValue() in functions package to func GetValue(), because, only that way the func will be visible to other packages. See here for more info.

File 1: main.go (located in MyProj/main.go)

package main


import (
"fmt"
"MyProj/functions"
)


func main(){
fmt.Println(functions.GetValue())
}

File 2: functions.go (located in MyProj/functions/functions.go)

package functions


// `getValue` should be `GetValue` to be exposed to other packages.
// It should start with a capital letter.
func GetValue() string{
return "Hello from this another package"
}
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Export function getValue by making 1st character of function name capital, GetValue

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In Go packages, all identifiers will be exported to other packages if the first letter of the identifier name starts with an uppercase letter.

=> change getValue() to GetValue()

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you can write 

import(
functions "./functions"
)
func main(){
c:= functions.getValue() <-
}

If you write in gopath write this import functions "MyProj/functions" or if you are working with Docker

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  • you need to create a go.mod file in the root directory of your project: go mod init module_name
  • the name of exposed function should start with capital letter
    import(
"module_name/functions"
)
func main(){
functions.SomeFunction()
}

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