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Notes
The intent of the Proxy pattern [Gamma+1995] is given as Provide a surrogate or placeholder for another object to control access to it. The alternative names Surrogate [Taligent1994] and Ambassador [Coplien1992] are also suggestive of the basic concept behind this pattern. [Taligent1994] provides a detailed taxonomy of surrogates based on their structure and intent. Pointers conventionally represent a level of indirection to a target; structurally this is a feature shared with Proxy classes. In C++ the Smart Pointer idiom builds on the understood protocol for pointers, specialising the Proxy pattern for certain examples where access control takes the same form for all operations. The essential features of a Smart Pointer are its dereferencing operations: through overloading, operator* and operator-> are supported. The operator* typically returns a reference rather than a value, and the operator-> must return something that in turn supports an operator->, such as a raw pointer. It is normally the responsibility of an object user to deal explicitly with the ownership and lifetime of objects. The standard auto_ptr template simplifies particular cases: heap object whose lifetime should be bound safely to an enclosing scope; exception safe transfer of object ownership through arguments or return values. The design of the standard auto_ptr has evolved through many unsatisfactory compromises to the point that some of its semantics and its full interface are less than intuitive. However, it is standard and the const auto_ptr idiom [Sutter2000] allows it to be used simply and in a manner closer to its original intended purpose.
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