Refactoring Boolean Flag Parameters

TL;DR

Explanation

function createUser($name, true, false, true) — what do those booleans mean? Boolean parameters (flag arguments) make call sites unreadable. Refactoring options: (1) Replace with enums/named constants, (2) Split into separate functions (createAdminUser, createGuestUser), (3) Use options object/named arguments, (4) Builder pattern for complex construction. PHP 8.0 named arguments partially solve the readability issue at call sites but don't fix the function signature. Martin Fowler's 'Remove Flag Argument' refactoring addresses this systematically.

Common Misconception

Why It Matters

Common Mistakes

• Adding boolean params to extend existing functions instead of adding new ones.
• Using boolean to toggle completely different behaviour — should be separate functions.
• Not using named arguments (PHP 8) at minimum to document existing boolean params.

Code Examples

createUser('Paul', true, false, true); // What are these booleans?

function createUser(string $name, bool $isAdmin, bool $sendEmail, bool $active) {}

// Option 1: Named enum
enum UserRole { case Admin; case Guest; }
createUser('Paul', UserRole::Admin);

// Option 2: Separate functions
createAdminUser('Paul');
createGuestUser('Paul');

// Option 3: Options object
createUser('Paul', new UserOptions(role: UserRole::Admin, active: true));

References

• ↗ https://refactoring.guru/refactoring/catalog

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