Essential Commands

go mod init <module>          # Initialize new module
go mod tidy                   # Add missing, remove unused
go test -race ./...          # Run with race detector
go test -cover ./...         # Show coverage
golangci-lint run            # Run all linters
govulncheck ./...            # Check vulnerabilities

Critical Patterns

// 1. Always check errors
result, err := someFunc()
if err != nil {
    return fmt.Errorf("operation failed: %w", err)  // Wrap with context
}

// 2. Use context for cancellation
func processData(ctx context.Context, data []string) error {
    for _, item := range data {
        select {
        case <-ctx.Done():
            return ctx.Err()  // Respect cancellation
        default:
            // Process item
        }
    }
    return nil
}

// 3. Defer cleanup immediately
file, err := os.Open("file.txt")
if err != nil {
    return err
}
defer file.Close()  // Defer right after open

// 4. Table-driven tests
func TestAdd(t *testing.T) {
    tests := []struct {
        name string
        a, b int
        want int
    }{
        {"positive", 1, 2, 3},
        {"negative", -1, -2, -3},
    }
    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            if got := Add(tt.a, tt.b); got != tt.want {
                t.Errorf("Add() = %v, want %v", got, tt.want)
            }
        })
    }
}

Rust Quick Reference

Essential Commands

cargo new my-project          # Create new project
cargo build --release         # Build optimized
cargo test                    # Run tests
cargo clippy                  # Linting
cargo fmt                     # Format code
cargo audit                   # Security audit

Critical Patterns

// 1. Ownership - each value has one owner
let s1 = String::from("hello");
let s2 = s1;  // s1 moved to s2
// println!("{}", s1);  // Error: value borrowed after move

// 2. Borrowing - references don't take ownership
fn calculate_length(s: &String) -> usize {
    s.len()
}
let s1 = String::from("hello");
let len = calculate_length(&s1);
println!("{} has length {}", s1, len);  // s1 still valid

// 3. Result for error handling
fn parse_number(s: &str) -> Result<i32, ParseIntError> {
    s.parse::<i32>()
}

// Use ? for propagation
fn read_file(path: &str) -> Result<String, std::io::Error> {
    let contents = std::fs::read_to_string(path)?;
    Ok(contents)
}

// 4. Option for nullable values
fn find_user(id: u32) -> Option<User> {
    if id == 0 { None } else { Some(User { id }) }
}

Go Error Handling

// Sentinel errors
var ErrNotFound = errors.New("not found")

// Custom error types
type ValidationError struct {
    Field string
    Issue string
}

func (e *ValidationError) Error() string {
    return fmt.Sprintf("validation failed on %s: %s", e.Field, e.Issue)
}

// Error wrapping
if err != nil {
    return fmt.Errorf("failed to process user %s: %w", id, err)
}

// Error checking
if errors.Is(err, ErrNotFound) { /* handle */ }
var valErr *ValidationError
if errors.As(err, &valErr) { /* handle */ }

Rust Error Handling

use thiserror::Error;

#[derive(Error, Debug)]
pub enum AppError {
    #[error("User not found: {0}")]
    NotFound(String),
    
    #[error("Database error: {0}")]
    Database(#[from] sqlx::Error),
    
    #[error("Invalid input: {0}")]
    Validation(String),
}

// Use anyhow for applications, thiserror for libraries
fn process_user(id: &str) -> anyhow::Result<User> {
    let user = find_user(id)
        .ok_or_else(|| anyhow::anyhow!("User {} not found", id))?;
    Ok(user)
}

Detailed References

Go Patterns: See references/go-patterns.md for concurrency, interfaces, testing
Rust Patterns: See references/rust-patterns.md for ownership, lifetimes, async

Use Case	Go	Rust
Web services, APIs	✅ Excellent	✅ Good
CLI tools	✅ Excellent	✅ Excellent
Systems programming	✅ Good	✅ Excellent
Memory-critical apps	⚠️ GC overhead	✅ Zero-cost
Concurrency	✅ Goroutines	✅ Fearless
Learning curve	✅ Easy	⚠️ Steeper

go-rust-systems

Go & Rust Systems Programming

When to Use Which

Go Quick Reference