How Do I Reference Go Modules from Outside the GOPATH?

Referencing Modules from Non-GOPATH Directories

The introduction of Go modules in Go 1.11 introduced changes in the referencing of modules and packages from non-GOPATH directories.

Old Way

Traditionally, Go modules were required to reside within the GOPATH. Modules and packages within this directory could be imported using the following syntax:

import (
    "github.com/username/modulename/subpackage"
)

New Way

With Go modules, this approach has changed. Packages can now reside outside of GOPATH. To reference a package from another directory:

Initializing a Module

Initialize a new module using the go mod init command:

go mod init github.com/username/modulename

This creates go.mod and go.sum files in the current directory.

Import Statements

Use import statements to reference packages from other directories. For example, if Module2 is located at /root/module2, and contains a package named module2, the import statement in Module1 will be:

import (
    "github.com/username/module2"
)

File Structure

Assuming the following file structure:

\root
└── module1
    ├── go.mod
    └── main.go

└── module2
    ├── go.mod
    └── module2.go

go.mod Files

Module1:

module github.com/username/module1

require (
    github.com/username/module2 v0.0.1
)

Module2:

module github.com/username/module2

go 1.13

main.go (Module1)

package main

import (
    "fmt"
    "github.com/username/module2"
)

func main() {
    fmt.Println(module2.Name())
}

module2.go (Module2)

package module2

import "fmt"

func Name() string {
    return "Module 2"
}

By following these steps, you can reference modules from non-GOPATH directories, enabling the reuse of code and modularity in Go projects.

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