Using the striger tool in Golang

Name: Go meetup
Venue: Deepsource office
Date: 14th Oct 2022

The Stringer interface

• It's an interface defined by the fmt package

• fmt and a lot of other packages look for implementations of this to print values

type Stringer interface {
  String() string
}

Example

type StatusCode int

const (
  statusOK                StatusCode = 200
  statusInternalServerErr StatusCode = 500
)

func main() {
  fmt.Println(statusOK)
  fmt.Println(statusInternalServerErr)

  // Output:
  // 200
  // 500
}

Example

type StatusCode int

func (c StatusCode) String() string {
  switch c {
  case 200:
    return "Status OK"
  case 500:
    return "Internal server error"
  default:
    return "Unknown status"
  }
}

const (
  statusOK                StatusCode = 200
  statusInternalServerErr StatusCode = 500
)

func main() {
  fmt.Println(statusOK)
  fmt.Println(statusInternalServerErr)

  // Output:
  // Status OK
  // Internal server error
}

Where is this useful ?

• Logging/Telemetry -> Numbers like 1, 2, 3 are not very useful while debugging

• Comparison with user input

  status := req.UserInput("http_status") // string value
  if status == statusOK.String() {
    // do stuff
  }
  

What is Stringer (the CLI tool) ?

• A CLI tool that auto-generate the String() method for a given int type

  go install golang.org/x/tools/cmd/stringer@latest
  

• Part of the gopls, goimports, gofmt gang

Demo

Challenge

What if I have multiple types and multiple sub-packages ?

Do I need to go and run stringer in all the sub-directories and for all types separately ?

Go generate

A Go command that helps you run tools that generate code

It looks for special comments like this:

package main 

//go:generate <command>

func main() {

}

ref: https://go.dev/blog/generate

Demo

Things to remember

• To run go generate as a part of your build/test/... workflows
  Because go build might NOT fail

  test:
    go generate ./... && go test -v ./...
  
  build:
    go generate ./... && go build
  

• go generate does NOT guaranty the order of execution

Thank you