GoLang Tutorial - Modules 0 (Using External Go Modules from GitHub)

In this post, we'll reverse a string in our main package where we call String function. The function is in reverse package that we can download from go_tutorial.

To use an external module, we need to do the following:

1. Import it:

   import "github.com/einsteinish/go_tutorial/string_util"



2. Call the code from the module:

   reversedString := reverse.String("Hello, world!")



3. Downloaded it: via either go mod tidy or go get github.com/einsteinish/go_tutorial/string_util

Here is the code, hello_world.go:

package main

import (
    "fmt"
    "github.com/einsteinish/go_tutorial/string_util"
)

func main() {
    reversedString := reverse.String("Hello, world!")
    fmt.Println(reversedString) // Output: !dlrow ,olleH
}

$ go mod init hello
go: creating new go.mod: module hello
go: to add module requirements and sums:
        go mod tidy    

go.mod:

module hello

go 1.21.4

To import the module, we can do either one of following two:

1. go mod tidy checks the imports used in our code and fetches the module if not fetched already.

   $ go mod tidy
   go: finding module for package github.com/einsteinish/go_tutorial/string_util
   go: found github.com/einsteinish/go_tutorial/string_util in github.com/einsteinish/go_tutorial v0.0.0-20231115000907-59bccb90e58f
   

   
   

   We can see go.mod has been updated:

   module hello
   
   go 1.21.4
   
   require github.com/einsteinish/go_tutorial v0.0.0-20231115000907-59bccb90e58f    
   



2. go get will fetch the module and download it and make it available for our project to use.

   $ go get github.com/einsteinish/go_tutorial/string_util
   go: added github.com/einsteinish/go_tutorial v0.0.0-20231115000907-59bccb90e58f
   

   
   

   We can see go.mod has been updated:

   module hello
   
   go 1.21.4
   
   require github.com/einsteinish/go_tutorial v0.0.0-20231115000907-59bccb90e58f // indirect  
   

Regardless of our choice, we get an identical output:

$ go run hello_world.go 
!dlrow ,olleH    

FYI:

Files we have created so far:

module hello

go 1.21.4

require github.com/einsteinish/go_tutorial v0.0.0-20231115000907-59bccb90e58f // indirect

github.com/einsteinish/go_tutorial v0.0.0-20231115000907-59bccb90e58f h1:FOZzpCJzzJyK2hhYYVTWNpGSauFwvv+ZPVer+vHWmQQ=
github.com/einsteinish/go_tutorial v0.0.0-20231115000907-59bccb90e58f/go.mod h1:vdljcg3Z2tZ56EhjeU/+nbjIWq8oV/ztSx2ZvXqgt8s=

package main

import (
    "fmt"
    "github.com/einsteinish/go_tutorial/string_util"
)

func main() {
    reversedString := reverse.String("Hello, world!")
    fmt.Println(reversedString) // Output: !dlrow ,olleH
}

Go Tutorial

1. GoLang Tutorial - HelloWorld
2. Calling code in an external package & go.mod / go.sum files
3. Workspaces
4. Workspaces II
5. Visual Studio Code
6. Data Types and Variables
7. byte and rune
8. Packages
9. Functions
10. Arrays and Slices
11. A function taking and returning a slice
12. Conditionals
13. Loops
14. Maps
15. Range
16. Pointers
17. Closures and Anonymous Functions
18. Structs and receiver methods
19. Value or Pointer Receivers
20. Interfaces
21. Web Application Part 0 (Introduction)
22. Web Application Part 1 (Basic)
23. Web Application Part 2 (Using net/http)
24. Web Application Part 3 (Adding "edit" capability)
25. Web Application Part 4 (Handling non-existent pages and saving pages)
26. Web Application Part 5 (Error handling and template caching)
27. Web Application Part 6 (Validating the title with a regular expression)
28. Web Application Part 7 (Function Literals and Closures)
29. Building Docker image and deploying Go application to a Kubernetes cluster (minikube)
30. Serverless Framework (Serverless Application Model-SAM)
31. Serverless Web API with AWS Lambda
32. Arrays vs Slices with an array left rotation sample
33. Variadic Functions
34. Goroutines
35. Channels ("<-")
36. Channels ("<-") with Select
37. Channels ("<-") with worker pools
38. Defer
39. GoLang Panic and Recover
40. String Formatting
41. JSON
42. SQLite
43. Modules 0: Using External Go Modules from GitHub
44. Modules 1 (Creating a new module)
45. Modules 2 (Adding Dependencies)
46. AWS SDK for Go (S3 listing)
47. Linked List
48. Binary Search Tree (BST) Part 1 (Tree/Node structs with insert and print functions)
49. Go Application Authentication I (BasicAuth, Bearer-Token-Based Authentication)
50. Go Application Authentication II (JWT Authentication)