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 :=

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

Inside functions, group adjacent vars even if unrelated:

Constants and iota

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

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:

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"}

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).

Initializing Maps

make() visually distinguishes empty-but-initialized from nil. Use size hints when the count is known.

Raw String Literals

Use backtick strings to avoid hand-escaped characters:

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

Prefer any Over interface{}

Go 1.18+: use any instead of interface{} in all new code.

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) as names. Use go vet to detect.

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