go-declarations

Go Declarations and Initialization

Compatibility: Examples may use any, which requires Go 1.18+.

Resource Routing

• references/SCOPE.md - Read when deciding between var, :=, if-init, and narrow variable scope.
• references/IOTA.md - Read when designing constants or enum-like values.
• references/INITIALIZATION.md - Read when initializing structs, maps, zero values, or pointers.
• references/LITERALS.md - Read for composite literal formatting and keyed-field tradeoffs.
• references/STRUCTS.md - Read when designing or initializing structs.
• references/SHADOWING.md - Read when a declaration may shadow a builtin or outer variable.

Quick Reference: var vs :=

Context	Use	Example
Top-level	var (always)	var _s = F()
Local with value	:=	s := "foo"
Local zero-value (intentional)	var	var filtered []int
Type differs from expression	var with type	var _e error = F()

---

Group Similar Declarations

Group related var, const, type in parenthesized blocks. Separate unrelated declarations into distinct blocks.

// 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).

---

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. Move constants into functions when only used there.

---

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"}