Unused Function Parameter

ID

swift.unused_function_parameter

Severity

info

Remediation Complexity

medium

Remediation Risk

low

Remediation Effort

medium

Resource

Code Smell

Language

Swift

Tags

code-smell, dead-code

Description

Reports a function parameter whose internal name is never referenced from inside the function body. The function would behave identically with the parameter dropped (or renamed to the wildcard _, which already signals "intentionally ignored").

func greet(name: String, age: Int) {        // FLAW on `age`
    print("Hi \(name)")
}

func greet(name: String, age _: Int) {      // OK — explicitly ignored
    print("Hi \(name)")
}

Rationale

Unused parameters add noise to the function signature, mislead the reader into thinking the value matters, and silently survive refactors that should have dropped them. Swift offers _ as the conventional "this parameter exists for the protocol / API but is not consumed" marker, and code review should require its use.

Protocol method requirements (declarations without a body) and parameters whose internal name is already _ are not flagged.

Remediation

Drop the parameter when it is genuinely not needed, or rename the internal name to _ to keep the call-site label:

func greet(name: String) {
    print("Hi \(name)")
}

func greet(name: String, age _: Int) {
    print("Hi \(name)")
}

References