Separation of concerns

What it is

Separate HTTP, business rules, storage, and presentation responsibilities.

When to use it

Reduce coupling and allow business tests without a web request.

Syntax

HTTP boundary != domain rule != persistence != rendering

Example

// HTTP controller invokes an operation:
$result = $transferService->move($actor, $sourceId, $destinationId, $amountCents);
// Service accepts typed/domain inputs, not the whole Request.

Common mistakes

Moving a giant controller into a giant service does not establish clear responsibilities.

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