go-declarations

Go Declarations and Initialization 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() 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 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 ). 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 . Move constants into functions when only used there. 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 Scenario Use Example Empty, populated later make(map[K]V) m := make(map[string]int) Nil declaration var var m map[string]int Fixed entries at init Literal m := map[string]int{"a": 1} 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: // 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 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. // 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.