Long Parameter List

Also Known As

TL;DR

Explanation

Long parameter lists are fragile: callers must remember the order of arguments, optional parameters with defaults spread throughout are easy to mis-specify, and adding a new parameter breaks every call site. The common refactoring is to introduce a Parameter Object — a simple class or readonly struct that groups related parameters — so the method signature becomes function process(OrderData $order) instead of function process($id, $name, $qty, $price, $discount, $tax).

Common Misconception

Why It Matters

Common Mistakes

• Adding a new optional parameter every time behaviour needs to vary — use a parameter object or strategy instead.
• Boolean flag parameters that control internal branching — split into two separate functions.
• Not using constructor promotion for objects that are just bundles of related parameters.
• Accepting an array of 'options' instead of a typed parameter object — loses type safety and discoverability.

Code Examples

function createUser(
    string $name, string $email, string $role,
    bool $active, ?string $avatar, int $orgId
): User {}

// Introduce a parameter object
class CreateUserRequest {
    public function __construct(
        public readonly string  $name,
        public readonly string  $email,
        public readonly string  $role   = 'member',
        public readonly bool    $active = true,
        public readonly ?string $avatar = null,
        public readonly int     $orgId  = 0,
    ) {}
}

function createUser(CreateUserRequest $req): User {}

References

• ↗ https://refactoring.guru/smells/long-parameter-list

Tags

Related Terms