1
touch main.go

package main

import "fmt"

func main() {
	fmt.Println(helloworld())
}

touch helloworld.go

package main

func helloworld() string {
	return "hello world"
}

下command

go run main.go helloworld.go

同一層資料夾的go，package必須相同，例如範例兩隻package都是main

mkdir helloworld
mv helloworld.go ./helloworld

export GOPATH=/var/go1

vi ./helloworld/helloworld.go

package helloworld

func HelloWorld() string { // export必須為大寫
	return "hello world"
}

vi main.go

package main

import (
	"fmt"
	"github.com/go-training/test/helloworld" // 通常以{網域名}{帳戶名}{專案名稱}，一切皆以gopath的src下為路徑
)

func main() {
	fmt.Println(helloworld.HelloWorld()) // 引入package name去調用其func
}

四種import

import "github.com/go-training/test/helloworld"

{package Name}.{method name}()

2
別名

import {alias} "github.com/go-training/test/helloworld"

{alias}.{method name}()

3
use dot

import . "github.com/go-training/test/helloworld"

{method name}()

此時package會到main.go同層，直接呼叫method即可使用
不建議用此方法import，維護code會很麻煩

4
use underscore
vi ./helloworld/helloworld.go

package helloworld

import "fmt"

func init() {
	fmt.Println("init helloworld")
}
func HelloWorld() string { // export必須為大寫
	return "hello world"
}

vi main.go

package main

import (
	"fmt"
	_ "github.com/go-training/test/helloworld" // 通常以{網域名}{帳戶名}{專案名稱}，一切皆以gopath的src下為路徑
)

func main() {
	fmt.Println("eee") // 引入package name去調用其func
}