go-coding-standards

Go Coding Standards

Idiomatic Go conventions grounded in Effective Go, Go Code Review Comments, and production-proven idioms. All code MUST pass goimports, go vet, and staticcheck (or golangci-lint run) without errors.

1. Import Ordering

Group imports in this order, separated by blank lines:

import (
    // 1. Standard library
    "context"
    "fmt"
    "net/http"

    // 2. External packages
    "github.com/gorilla/mux"
    "log/slog"

    // 3. Internal/project packages
    "github.com/myorg/myproject/internal/service"
)

NEVER use dot imports. Use aliasing only to resolve conflicts.

2. Naming Conventions

Packages

• Short, lowercase, single-word names. No underscores, no camelCase.
• Name should describe what the package provides, not what it contains.
• Avoid generic names: util, common, helpers, misc, base.

Functions & Methods

• MixedCaps (exported) or mixedCaps (unexported). No underscores except in test files.
• Getters: use Name(), NOT GetName(). Setters: use SetName().
• Constructors: NewFoo() returns *Foo. If only one type in package: New().

Variables

• Short names in tight scopes: i, n, err, ctx.
• Descriptive names for wider scopes: userCount, retryTimeout.
• Prefix unexported package-level globals with _: var _defaultTimeout = 5 * time.Second.
• Do NOT shadow built-in identifiers (error, len, cap, new, make, close).

Interfaces

• Single-method interfaces: method name + -er suffix (Reader, Writer, Closer).
• Define interfaces where they are consumed, not where they are implemented.

3. Variable Declarations

Top-level

Use var for top-level declarations. Do NOT specify type when it matches the expression:

// ✅ Good
var _defaultPort = 8080
var _logger = slog.Default()

// ❌ Bad — redundant type
var _defaultPort int = 8080

Local

• Prefer := for local variables.
• Use var only when zero-value initialization is intentional and meaningful.

// ✅ Good — zero value is meaningful
var buf bytes.Buffer

// ✅ Good — short declaration
name := getUserName()

4. Struct Initialization

ALWAYS use field names. Never rely on positional initialization:

// ✅ Good
user := User{
    Name:  "Alice",
    Email: "alice@example.com",
    Age:   30,
}

// ❌ Bad — positional, breaks on field reordering
user := User{"Alice", "alice@example.com", 30}

Omit zero-value fields unless clarity requires them:

// ✅ Good — zero values omitted
user := User{
    Name: "Alice",
}

5. Reduce Nesting

Handle errors and special cases first with early returns. Reduce indentation levels:

// ✅ Good — early return
func process(data []Item) error {
    for _, v := range data {
        if !v.IsValid() {
            log.Printf("invalid item: %v", v)
            continue
        }

        if err := v.Process(); err != nil {
            return err
        }

        v.Send()
    }
    return nil
}

Eliminate unnecessary else blocks:

// ✅ Good
a := 10
if condition {
    a = 20
}

// ❌ Bad
var a int
if condition {
    a = 20
} else {
    a = 10
}

6. Grouping and Ordering

Group related declarations:

const (
    _defaultPort    = 8080
    _defaultTimeout = 30 * time.Second
)

var (
    _validTypes  = map[string]bool{"json": true, "xml": true}
    _defaultUser = User{Name: "guest"}
)

Function ordering within a file:

1. Constants and variables
2. New() / constructor functions
3. Exported methods (sorted by importance, not alphabetically)
4. Unexported methods
5. Helper functions

Receiver methods should appear immediately after the type declaration.

7. Line Length

Soft limit of 99 characters. Break long function signatures:

func (s *Store) CreateUser(
    ctx context.Context,
    name string,
    email string,
    opts ...CreateOption,
) (*User, error) {

8. Defer Usage

Use defer for cleanup. It makes intent clear at the point of acquisition:

mu.Lock()
defer mu.Unlock()

f, err := os.Open(path)
if err != nil {
    return err
}
defer f.Close()

9. Enums

Start enums at 1 (or use explicit sentinel) so zero-value signals "unset":

type Status int

const (
    StatusUnknown Status = iota
    StatusActive
    StatusInactive
)

10. Use time Package Properly

• Use time.Duration for durations, NOT raw integers.
• Use time.Time for instants. Use time.Since(start) instead of time.Now().Sub(start).
• External APIs: accept int or float64 and convert internally.

// ✅ Good
func poll(interval time.Duration) { ... }
poll(10 * time.Second)

// ❌ Bad
func poll(intervalSecs int) { ... }
poll(10)

11. Receivers

Pick one receiver kind per type and use it for every method on that type. A type with both value and pointer methods has a method set that changes depending on how it is held, which is a bug waiting to happen.

Use a pointer receiver when any of these hold — and then use it everywhere:

• A method mutates the receiver
• The struct contains a sync.Mutex or any other field that must not be copied
• The struct is large enough that copying it per call is measurable
• Any other method on the type already needs a pointer receiver

Use a value receiver for small immutable types: time.Time-like value objects, enums, and types whose methods only read.

// ✅ Consistent — every method on *Buffer takes a pointer
func (b *Buffer) Write(p []byte) (int, error) { ... }
func (b *Buffer) Len() int                     { ... }

// ❌ Mixed — Len() on a value copies the mutex
func (b *Buffer) Write(p []byte) (int, error) { ... }
func (b Buffer) Len() int                      { ... }

Name the receiver one or two letters after the type (s *Server, b *Buffer). Never this or self. Keep the same name across every method on the type.

12. Struct Tags

Tags are strings the compiler does not check. A typo is silent.

// ✅ Good — backticks, no spaces after commas, explicit names
type User struct {
    ID        string    `json:"id" db:"id"`
    Email     string    `json:"email" db:"email" validate:"required,email"`
    CreatedAt time.Time `json:"created_at" db:"created_at"`
    password  string    `json:"-"` // never serialised
}

// ❌ Bad
type User struct {
    ID    string `json: "id"`        // space after the colon: tag is ignored
    Email string `json:"email,"`     // trailing comma
    Token string                     // no tag: marshals as "Token"
}

Rules:

• Tag every field of a type that crosses a serialisation boundary, including the ones whose name would happen to match.
• Use json:"-" for anything that must never leave the process. Do not rely on a field being unexported — an unexported field is skipped by encoding/json silently, which reads as an oversight rather than intent.
• omitempty omits zero values, so it cannot distinguish "absent" from "explicitly zero". Use a pointer or a wrapper type when that distinction carries meaning.
• go vet includes a structtag check. Run it — it catches the malformed cases above.

Verification Checklist

Before considering code complete:

1. goimports runs clean
2. go vet ./... passes
3. golangci-lint run passes (if configured)
4. No shadowed built-in identifiers
5. All imports properly grouped and ordered
6. Struct initializations use field names
7. No unnecessary nesting or else blocks
8. Receiver kind is consistent across every method on a type
9. Every serialised struct field carries an explicit tag