Golang导入包

Question

I have some problem with Golang and include package. I have that scructure

src/
├── hello_world
│   ├── hello.go
│   └── math
│       └── add.go

hello.go file contains this code:

package main

import (
    "fmt"
    math "hello_world/math"
)

func main() {
    fmt.Println("Hello World")
    x := math.add(6, 5)
}

and add.go

package math

func add(x, y int) int {
    return x + y
}

and when I do go run hello go I see:

evgen@laptop:~/go/src/hello_world$ go run hello.go 
# command-line-arguments
./hello.go:10: cannot refer to unexported name math.add
./hello.go:10: undefined: "hello_world/math".add

GOPATH:

evgen@laptop:~/go/src/hello_world$ echo $GOPATH
/home/evgen/go

How fix it? Thanks you!

Answer 1

Outside of a package only the exported identifiers can be reached and referred to, that is identifiers that start with an uppercase letter.

So the easiest fix is to export your math.add() function by changing its name to Add() in math.go:

func Add(x, y int) int {
    return x + y
}

And, of course, when you refer to it from the main.go:

x := math.Add(6, 5)

And as a side note, note that when importing your hello_world/math package you don't have to specify a new name to refer to its exported identifiers: by default it will be the last part of its import path, so this is equivalent to your imports:

import (
    "fmt"
    "hello_world/math"
)