Function Parameters

Periphery can identify unused function parameters. Instances of unused parameters can also be identified in protocols and their conforming declarations, as well as parameters in overridden methods.

Protocols

An unused parameter of a protocol function will only be reported as unused if the parameter is also unused in all implementations.

protocol Greeter {
    func greet(name: String)
    func farewell(name: String) // 'name' is unused
}

class InformalGreeter: Greeter {
    func greet(name: String) {
        print("Sup " + name + ".")
    }

    func farewell(name: String) { // 'name' is unused
      print("Cya.")
    }
}

Tip

You can ignore all unused parameters from protocols and conforming functions with the --retain-unused-protocol-func-params option.

Overrides

Similar to protocols, parameters of overridden functions are only reported as unused if they’re also unused in the base function and all overriding functions.

class BaseGreeter {
    func greet(name: String) {
        print("Hello.")
    }

    func farewell(name: String) { // 'name' is unused
        print("Goodbye.")
    }
}

class InformalGreeter: BaseGreeter {
    override func greet(name: String) {
        print("Sup " + name + ".")
    }

    override func farewell(name: String) { // 'name' is unused
        print("Cya.")
    }
}

Foreign Protocols & Classes

Unused parameters of protocols or classes defined in foreign modules (e.g. Foundation) are always ignored since you do not have access to modify the base function declaration.

fatalError Functions

Unused parameters of functions that simply call fatalError are also ignored. Such functions are often unimplemented required initializers in subclasses.

class Base {
    let param: String

    required init(param: String) {
        self.param = param
    }
}

class Subclass: Base {
    init(custom: String) {
        super.init(param: custom)
    }

    required init(param: String) {
        fatalError("init(param:) has not been implemented")
    }
}