Go Declarations and Initialization

Quick Reference: var vs :=

var

var _s = F()

:=

s := "foo"

var

var filtered []int

var

var _e error = F()

Read references/SCOPE.md when deciding between var and := in complex initialization patterns or multi-return assignments.

Group Similar Declarations

Group related

var

const

type

// Bad
const a = 1
const b = 2

// Good
const (
    a = 1
    b = 2
)

Inside functions, group adjacent vars even if unrelated:

var (
    caller  = c.name
    format  = "json"
    timeout = 5 * time.Second
)

Constants and iota

Start enums at one so the zero value represents invalid/unset:

const (
    Add Operation = iota + 1
    Subtract
    Multiply
)

Use zero when the default behavior is desirable (e.g.,

LogToStdout

Read references/IOTA.md when designing iota enums with bitmask patterns, byte-size constants, or String() methods.

Variable Scope

Use if-init to limit scope when the result is only needed for the error check:

if err := os.WriteFile(name, data, 0644); err != nil {
    return err
}

Don't reduce scope if it forces deeper nesting or you need the result outside the

if

Read references/SCOPE.md when working with top-level declarations or choosing between var and := for local variables.

Initializing Structs

• Always use field names (enforced by

  go vet

  ). Exception: test tables with ≤3 fields.
• Omit zero-value fields — let Go set defaults.
• Use

  var

  for zero-value structs:

  var user User

  not

  user := User{}

• Use

  &T{}

  over

  new(T)

  :

  sptr := &T{Name: "bar"}

Read references/STRUCTS.md when initializing structs with many fields, building slices of struct pointers, or choosing single-line vs multi-line format.

Composite Literal Formatting

Use field names for external package types. Match closing brace indentation with the opening line. Omit repeated type names in slice/map literals (

gofmt -s

Read references/INITIALIZATION.md when working with complex composite literals, cuddled braces, or zero-value field decisions.

Read references/LITERALS.md when formatting complex composite literals.

Initializing Maps

make(map[K]V)

m := make(map[string]int)

var

var m map[string]int

m := map[string]int{"a": 1}

make()

Raw String Literals

Use backtick strings to avoid hand-escaped characters:

// Bad
wantError := "unknown name:\"test\""

// Good
wantError := `unknown name:"test"`

Ideal for regex, SQL, JSON, and multi-line text.

Prefer

any

Over

interface{}

Go 1.18+: use

any

interface{}

Avoid Shadowing Built-In Names

Never use predeclared identifiers (

error

string

len

cap

append

copy

new

make

close

delete

panic

recover

any

true

false

nil

iota

go vet

// Bad — shadows the builtin
var error string

// Good
var errorMessage string

Read references/SHADOWING.md when debugging issues where := creates new variables that shadow outer scope.

Related Skills

• Naming conventions: See go-naming when choosing variable names, constant names, or deciding name length by scope
• Data structures: See go-data-structures when choosing between

  new

  and

  make

  , or initializing slices and maps
• Control flow scoping: See go-control-flow when using if-init,

  :=

  redeclaration, or avoiding variable shadowing
• Capacity hints: See go-performance when pre-allocating maps or slices with known sizes