A software design pattern often used to restrict access to an object is:

CONCEPT — A structural design pattern can interpose a stand-in between a client and a real object while preserving the interface the client expects.

The stand-in mediates requests before they reach the real object. When that mediation checks permissions or denies operations, it is providing access control.

APPLICATION — Consider a document service with a read() operation that should be available only to authorized users.

1. The client calls read() on an object that implements the document interface.

2. A stand-in implementing the same interface receives the call first and checks the caller’s permissions.

3. The stand-in forwards an authorized call to the real document object and rejects an unauthorized call.

4. This same-interface surrogate that controls access is a protection proxy, so the applicable pattern is proxy.

CROSS-CHECK / CONTRAST — Compare the intent of each offered term.

• Adapter translates one interface into another expected interface.

• Decorator keeps the interface while adding responsibilities to an object.

• Delegation transfers responsibility for an operation to another object.

• Proxy keeps the subject interface while mediating access to the real subject.

RESULT — The pattern used to restrict access to an object is proxy.