modules

Question 1

What is a Go Module?

Answer 1

A collection of related Go packages with versioned dependencies

Key Files:
* go.mod (declares module path and dependencies)
* go.sum (records cryptographic checksums)

module github.com/yourname/project

go 1.21

require (
    github.com/pkg/errors v0.9.1
    golang.org/x/sync v0.3.0
)

Question 2

Initializing a Module

Answer 2

go mod init github.com/yourname/project

What it does:
Creates a go.mod file in your project root.
Rule:
Module path should match your code’s import path.

Question 3

Adding Dependencies

Answer 3

Automatically:
Just import in code and run:

go mod tidy

Manually:

go get github.com/pkg/errors@v0.9.1

Key Flags:
@latest - gets newest version
@v1.2.3 - specific version

Question 4

go mod tidy

Answer 4

Purpose:

Adds missing dependencies

Removes unused dependencies

Updates go.mod/go.sum
Always run this:
After changing imports or before committing.

Question 5

Upgrading/Downgrading

Answer 5

Check versions:
go list -m -versions github.com/pkg/errors

Upgrade:
go get github.com/pkg/errors@latest

Downgrade:
go get github.com/pkg/errors@v0.8.1

Question 6

Vendor Directory

Answer 6

Create vendor/:
go mod vendor

Use vendor/:
go build -mod=vendor

Purpose:
Stores dependency copies locally for reproducibility.

Question 7

Version Selection

Answer 7

How Go chooses versions:
1. Highest compatible semver tag (e.g., v2.3.4)
2. Pseudo-versions (e.g., v0.0.0-20231012000000-abc123)
Key Terms:
* Minimal version selection (MVS)
* Semantic Import Versioning (major versions ≥2 change import paths)

Question 8

Replacing Dependencies

Answer 8

In go.mod:

replace ( github.com/old/mod => ../local/mod golang.org/x/net => github.com/golang/net v0.7.0 )

Use Cases:
* Local development
* Forked dependencies

Question 9

Module Proxy

Answer 9

Default Proxy:
proxy.golang.org (Google-run)
Environment Variables:

GOPROXY=https://proxy.golang.org,direct

GOPRIVATE=github.com/yourcompany/* (skip proxy for private repos)

Question 10

Key Commands Cheat Sheet

Answer 10

Command Purpose
go mod init Initialize new module
go mod tidy Sync dependencies
go get -u Update dependencies
go list -m all View all dependencies
go mod why Explain why a dependency exists
go mod graph Print dependency graph
Golden Rule:
Always commit both go.mod and go.sum to version control!