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  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

<concept id="GUID-772DFFA1-4BBC-516F-909D-47CB773760F5" xml:lang="en"><title>Packages as type-safe descriptors</title><shortdesc>Describes the package function to transfer data in correct

structure. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>Descriptors are often used as the basis of data transfer within

Symbian platform. For example, inter-thread data transfer is specified

in terms of transferring data from a descriptor valid in the context

of one thread, to a descriptor valid in the context of another.</p>

<p>Data to be transferred almost always has a well defined structure

and it is important that the receiver of the data has some guarantee

that the correct structure has been passed. This is type safety.</p>

<p>A package <i>is</i> a descriptor and also acts as a wrapper around

it. It allows objects and data structures to be represented by descriptors

in a type safe way. Objects are either contained within a modifiable

buffer descriptor or are represented by pointer descriptors.</p>

<p>A package class is templated, the template parameter being the

type of the object represented. The use of a template provides the

required type safety.</p>

</conbody><related-links>

<link href="GUID-79BAF19D-F003-5468-9C01-6E918B06C36D.dita">

<linktext>Descriptor concepts</linktext></link>