R class

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Article

Created: tote_b5 (22 Mar 2007)

Last edited: hamishwillee (26 Jul 2012)

Introduction

R classes are proxies for objects owned elsewhere. There are two main motivations for this:

The real object is owned by a server in a different thread or address space, or
the real object’s implementation must be hidden from the client.

The following are key characteristics of R objects:

They contain a handle that is used to pass on requests to other objects
They are opened using an "open" function particular to the R class, and closed using a "close" function particular to the class. An R object must be closed once if it has been opened. Generally, the resource associated with an R object is closed automatically if the thread which opened the object terminates.
They have no explicit constructor, destructor, copy constructor or assignment operator.

It's also worth noting that

There is no common base class for all R classes
The initialisation function has a variety of names: also possible are Open(), Create(), Allocate(), etc.
The termination function has a variety of names: also possible are Close(), Destroy(), Free(), etc.
Since R classes own external resources, there is a requirement for cleanup: this is handled in various ways depending on the class.