Boolean Return Nil

ID

swift.boolean_return_nil

Severity

low

Remediation Complexity

medium

Remediation Risk

low

Remediation Effort

medium

Resource

Code Smell

Language

Swift

Tags

code-smell, optionals

Description

Reports a return nil statement inside a function whose declared return type is Bool? (or Optional<Bool>). The caller is now forced to distinguish three states — true, false, nil — and cannot tell which case the implementation meant by returning nil.

func isReady() -> Bool? {
    if Bool.random() { return true }
    return nil                          // FLAW
}

func isReady() -> Bool { return Bool.random() }   // OK
func findId() -> Int? { return nil }              // OK — non-Bool optional

Rationale

A Bool already encodes exactly two states. Promoting it to Bool? and returning nil collapses an extra "unknown" state into the same type without naming it. Callers tend to forget the nil branch, or write x ?? false and silently lose information.

Remediation

Pick one of:

  • Return a plain Bool and pick a default for the unknown case.

  • Throw an error to signal "I cannot decide".

  • Model the unknown state explicitly with an enum.

enum Readiness { case yes, no, unknown }
func isReady() -> Readiness { ... }

func isReady() throws -> Bool { ... }

References