Joe Wood Notes

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Compile

To compile and execute a basic Go program, use the go build and go run commands Example: Basic Go Compilation:

// main.go
package main

import "fmt"

func main() {
    fmt.Println("Hello, Go!")
}

To compile and run:

go build -o myprogram main.go
./myprogram

Alternatively, you can directly execute the Go program without compiling:

go run main.go

Common Compilation Tools:

• go fmt – Formats Go code according to Go standards.
• go vet – Analyzes code for potential issues.
• golint – Provides stylistic recommendations.

go fmt main.go
go vet main.go
golint main.go

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Modules

Creating a Reusable Module: Go modules allow you to manage dependencies and organize reusable code.

Initialize a Module:

go mod init example.com/mymodule

This creates a go.mod file:

module example.com/mymodule

go 1.20

To defining an Exported Function:

// mymodule/mylib.go
package mymodule

import "fmt"

// Exported function (must start with uppercase letter)
func SayHello(name string) {
    fmt.Printf("Hello, %s!\n", name)
}

Using the Module in Another File:

package main

import (
    "example.com/mymodule"
)

func main() {
    mymodule.SayHello("Alice")
}

Managing Dependencies:

• Add a dependency: go get example.com/somepackage
• Remove unused dependencies: go mod tidy
• List dependencies: go list -m all

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Import Package

To add an External Package. Use go get to install third-party packages.

Example: Using github.com/fatih/color for Colored Output:

go get github.com/fatih/color

Import and use it:

package main

import (
    "github.com/fatih/color"
)

func main() {
    color.Red("This is a red message")
}

Upgrading a Package:

go get -u github.com/fatih/color

Locking to a Specific Version:

go get github.com/fatih/color@v1.12.0

Checking and Managing Dependencies:

Go provides mechanisms to lock dependencies to specific versions and ensure reproducible builds.

Generating and Committing a Lockfile - Go automatically maintains a go.sum file, which records cryptographic checksums of dependencies. This file should be committed to version control to ensure consistency across builds.

git add go.sum
git commit -m "Add go.sum to track dependency checksums"

Checking Installed Modules:

go list -m all  # List all modules in use

Tidying Dependencies:

go mod tidy  # Remove unused dependencies and update go.mod and go.sum

Verifying Module Integrity:

go mod verify  # Verify checksums in go.sum against downloaded modules

go list -m all         # List all modules
go mod tidy           # Remove unused dependencies
go mod verify         # Verify checksums

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Publish a Package

Publishing a Go Package for External Use. To publish a package:

1. Create a public repository on GitHub/GitLab.
2. Ensure a valid go.mod file.
3. Push the module to a repository.

git init
git remote add origin https://github.com/username/mymodule.git
git add .
git commit -m "Initial commit"
git push -u origin main

Tagging a Release:

git tag v1.0.0
git push origin v1.0.0

Using the Published Module:

go get github.com/username/mymodule@v1.0.0

Example: Importing and Using the Published Module:

package main

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

func main() {
    mymodule.SayHello("Bob")
}

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Tests

Adding Tests to a Package. Go includes a built-in testing package for unit testing. Example: Writing a Test:

// mymodule/mylib.go
package mymodule

func Add(a, b int) int {
    return a + b
}

// mymodule/mylib_test.go
package mymodule

import "testing"

func TestAdd(t *testing.T) {
    result := Add(2, 3)
    expected := 5
    if result != expected {
        t.Errorf("Expected %d but got %d", expected, result)
    }
}

Running Tests:

go test ./...

Running Tests with Coverage:

go test -cover ./...

Integrating Tests into CI/CD. To automate testing in CI pipelines, add:

go test ./... && go vet ./...

to your build pipeline configuration.

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Custom Tools

Incorporating Code Generation Tools. Some Go projects require automatic code generation, such as OpenAPI or gRPC.

Installing stringer for Enum String Generation

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

Using it in Go:

// Define an enum
package main

//go:generate stringer -type=Animal
type Animal int

const (
    Dog Animal = iota
    Cat
    Fish
)

Generate code:

go generate ./...

Generating OpenAPI with oapi-codegen:

go install github.com/deepmap/oapi-codegen/cmd/oapi-codegen@latest
oapi-codegen -generate types -o types.gen.go api.yaml

Automating Builds with a Custom Script. Example build.sh script:

#!/bin/bash
set -e

go fmt ./...
go vet ./...
go test ./...
go build -o myapp main.go

echo "Build successful!"

Run:

chmod +x build.sh
./build.sh