Unused Declaration

ID

swift.unused_declaration

Severity

low

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Dead Code

Language

Swift

Tags

dead-code, suspicious-code, unused-code

Description

Reports a top-level private or fileprivate declaration — a class, struct, enum, protocol, function, var or let — that is never referenced anywhere else in the same file. Since the visibility scope is the file itself, an absence of references in the file proves the declaration is dead code that the developer most likely forgot to delete.

private func deadHelper() {       // FLAW — never called
    print("unused")
}

private struct DeadBox {          // FLAW — never instantiated
    let value: Int = 0
}

private var unusedFlag = false    // FLAW — never read

private func usedHelper() { ... } // OK — called below
usedHelper()

Rationale

Dead code accumulates as refactors land. A top-level private symbol that no one in the file references serves no purpose: removing it does not change behaviour, and keeping it forces every future reader to re-prove that nothing reaches it. The rule limits itself to file-local visibility (private, fileprivate) so that no project-wide analysis is required — for higher visibilities the declaration may be used by other files in the module or by other modules, and a single-file rule cannot rule that out.

Remediation

Delete the unused declaration, or — if you actually meant to reach it from another file — promote its visibility to internal or higher.

The following declarations are intentionally skipped:

  • @objc, @IBAction and @IBOutlet — reachable from Objective-C and Interface Builder, invisible to source-level analysis.

  • Computed and observable properties.

  • Initializers.

References