Disguised as a friendly shortcut is another coupling smell.

TL;DR: Optional Arguments generate a hidden coupling in the name of smaller code.

Problems

• Coupling

• Unexpected results

• Side effects

• Ripple Effect

• In languages with optional arguments but limited to basic types, we need to set a flag and add an accidental IF (another smell).

Solutions

1. Make arguments explicit.
2. All function calls must have same arity.
3. Use Named Parameters if your language supports them.