Remove Parameter

Problem

A method takes a parameter it ignores. It was used once, or added "in case", and now every caller has to compute and pass a value that changes nothing. Readers assume it matters.

Solution

Remove the unused parameter from the method and from every call site.

Before

function scheduleReminder(
  appointment: Appointment,
  leadMinutes: number,
  timezone: string, // unused since reminders moved to UTC
  channel: "sms" | "email",
): Job {
  const runAt = new Date(appointment.startsAt.getTime() - leadMinutes * 60_000);
  return queue.enqueue("reminder", { appointmentId: appointment.id, channel }, runAt);
}

scheduleReminder(appt, 60, clinic.timezone, "sms");

After

function scheduleReminder(
  appointment: Appointment,
  leadMinutes: number,
  channel: "sms" | "email",
): Job {
  const runAt = new Date(appointment.startsAt.getTime() - leadMinutes * 60_000);
  return queue.enqueue("reminder", { appointmentId: appointment.id, channel }, runAt);
}

scheduleReminder(appt, 60, "sms");

Why

• A signature is a contract. Every parameter in it claims the method depends on that value.
• Callers stop computing values that are thrown away, which sometimes removes whole lookups.

Steps

1. Confirm the parameter is unused in the body and in every override and implementation. A parameter unused in the base class may be used in a subclass.
2. If the method is overridden or implements an interface, change all declarations together.
3. If your tooling has a safe "change signature" refactoring, use it. Run the tests.
4. Otherwise create a new method without the parameter, make the old one delegate to it, and move callers over a few at a time. Run the tests after each batch.
5. Delete the old signature when nothing calls it.

Watch out

• Do not remove a parameter required by an interface, callback type or framework hook (Express middleware next, event handler signatures). Prefix it with _ to signal it is intentionally unused.
• Positional removal in JavaScript shifts later arguments. Callers passing values by position will send the wrong value into the wrong slot without a type error if the types match. Use the type checker, and update all callers in one change.
• Public APIs need a deprecation period. Keep an overload that accepts and ignores the old argument.
• Check whether computing the argument had side effects at the call site that callers still rely on.
• The inverse technique is Add Parameter.

Related

• Inverse: Add Parameter.
• Fixes Long Parameter List, Speculative Generality and Dead Code.
• When the value is still needed but derivable, use Replace Parameter with Method Call.

Agent checklist

• The parameter is unused in every override and implementation.
• It is not required by an external interface, callback type or framework.
• All positional callers were updated in the same change.
• Argument expressions removed from call sites had no side effects callers depend on.