Blank identifier and predeclared identifiers

Canonical guidance

• _ is a write-only placeholder that discards a value
• names like len, make, error, nil, true, and false are predeclared by the language
• predeclared identifiers can still be shadowed, but doing so is usually confusing

Use when

• reading multi-value assignments
• reviewing imports kept only for side effects
• explaining built-in names

Avoid

• discarding errors casually
• naming locals len, error, or nil
• assuming _ creates storage or a usable variable

Preferred pattern

v, ok := m[key]
if !ok {
	return
}
_ = v

Anti-pattern

• using _ to ignore an error that should affect control flow

Explanation: This is tempting when plumbing code quickly, but ignored errors erase the branch that tells the program what actually happened.

Why

• _ and the predeclared names appear everywhere in Go code, so misunderstanding them has broad review impact