Use typed objects instead of loose arrays

How to do it

Give each shape a class, record or type with named, typed fields. A reader and an agent can then see every field without running the code. Typos fail at build time, not in production. A map with typed keys and values, such as Map<OrderId, Order>, is a typed shape too.

Example

// Bad: what keys does this array have, and what types?
function createInvoice(array $data): array { /* ... */ }

// Good: the type says it
final readonly class InvoiceRequest {
    public function __construct(public CustomerId $customer, public Money $amount, public DateTimeImmutable $due) {}
}
function createInvoice(InvoiceRequest $request): Invoice { /* ... */ }

// Bad
function createInvoice(data: any) { /* ... */ }

// Good
type InvoiceRequest = { readonly customer: CustomerId; readonly amount: Money; readonly due: Date };
function createInvoice(request: InvoiceRequest): Invoice { /* ... */ }

How to check

The type checker rejects untyped shapes. Examples are PHPStan at level 6 or higher, which requires array value types, TypeScript with strict, or mypy with --strict.