Flag Arguments

Boolean arguments that change function behavior.

“Boolean arguments that declare the function does two different things.” – Robert C. Martin

Signs of Use (Symptoms)

  • function render(data, isAdmin: boolean).
  • function process(order, dryRun: boolean).

Why it is bad (Consequences)

  • SRP: The function does two things depending on the flag.
  • Readability: render(data, true) - true for what?

Why it happens (Root Cause)

Adding a boolean is faster than creating a new function.

When it might be okay (Exceptions)

  • Very common, obvious flags (e.g., verbose: boolean for logging).

Explanation

Problem

save(user, isNew). If isNew is true, insert. If false, update.

The Flaw

The function does two distinct things. Split it.

Real world analogy

A button that says “Press for A or hold for B”. Just have two buttons.

Refactoring Solution

  • Remove Flag Argument: Create two separate functions: createUser(), updateUser().

Pros and Cons (of the Antipattern)

Pros (Why people do it) Cons (The price you pay)
  • One function
    		•
  • SRP violation
  • Confusing API
    		•

    Comparison

    • Related Antipatterns: Long Method.
    • Related Principles: SRP.

    Code example

    Typescript

    Bad (The Antipattern)

    Good (The Fix)