Unused Function Parameter

kotlin.unused_function_parameter

Severity

low

Remediation Complexity

medium

Remediation Risk

low

Remediation Effort

medium

Resource

Code Smell

Language

Kotlin

Description

Reports function parameters that are never referenced inside the function body. Parameters prefixed with _ and parameters of override functions are excluded.

Rationale

An unused parameter clutters the API, increases cognitive load for callers, and often indicates either dead code or a logic error (the author intended to use the parameter but forgot).

// Bad — b is declared but never used
fun add(a: Int, b: Int): Int { // FLAW
    return a
}

// Good — use both parameters
fun add(a: Int, b: Int): Int = a + b

// Also good — _ prefix marks deliberate non-use
fun onEvent(_event: String) {
    println("event fired")
}

Remediation

Either use the parameter in the body, remove it from the signature, or prefix the name with _ to signal that it is intentionally ignored.

References

Kotlin coding conventions