Variables and short declarations

Canonical guidance

• var declares variables explicitly and can omit an initializer
• := both declares and initializes, but only when at least one name is new in the current block
• scope and block boundaries decide whether code redeclares or shadows

Use when

• debugging no new variables on left side of :=
• deciding whether a declaration is new or reused
• reviewing initialization style

Avoid

• assuming := always creates a new variable
• mixing new and old names casually in long assignment lists
• using short declarations where the resulting scope becomes hard to read

Preferred pattern

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

Anti-pattern

• writing x, err := f() later in the same block when neither name is actually new

Explanation: This is tempting during refactors, but same-block short declarations have a strict rule and fail when no new non-blank identifier is introduced.

Why

• many common compile failures in Go are direct consequences of the short declaration rule