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Design patterns


Static diagram :

Static diagram

Description :

Type :  St  (Structural)
Intent : Provide a surrogate or placeholder for another object to control access to it.
Applicability : Proxy is applicable whenever there is a need for a more versatile or sophisticated reference to an object than a simple pointer. Here are several common situations in which the Proxy pattern is applicable :
1. A "remote proxy" provides a local representative for an object in a different address space. Coplien calls this kind of proxy an "Ambassador".
2. A "virtual proxy" creates expensive objects on demand.
3. A "protection proxy" controls access to the original object. Protection proxies are useful when objects should have different access rights.
4. A "smart reference" is a replacement for a bare pointer that performs additional actions when an object is accessed. Typical uses include
- counting the number of references to the real object so that it can be freed automatically when there are no more references (also called smart pointers).
- loading a persistent object into memory when it's first referenced.
- checking that the real object is locked before it's accessed to ensure that no other object can change it.

Pattern's participants :

Les têtes de mule