--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Symbian3/SDK/Source/GUID-38CF8A8E-4778-5374-8AC6-5F9486A2B7FB.dita	Thu Jan 21 18:18:20 2010 +0000
@@ -0,0 +1,38 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->
+<!-- This component and the accompanying materials are made available under the terms of the License 
+"Eclipse Public License v1.0" which accompanies this distribution, 
+and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->
+<!-- Initial Contributors:
+    Nokia Corporation - initial contribution.
+Contributors: 
+-->
+<!DOCTYPE concept
+  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
+<concept id="GUID-38CF8A8E-4778-5374-8AC6-5F9486A2B7FB" xml:lang="en"><title>The polymorphic
+interface DLL</title><shortdesc>A polymorphic interface DLL is one which is written to implement
+a programming interface defined elsewhere; for example, a device driver, an
+application or an OPL extension.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
+<p>The API is defined in terms of a single abstract class whose functions
+are declared as pure virtual. The DLL <i>implements</i> the API by defining
+and implementing a concrete class derived from that abstract class. The DLL
+exports a single function whose sole purpose is to create an object of the
+derived class type; this is always the function at ordinal 1 within the DLL.
+All other functions in the DLL are called through the virtual table mechanism
+(the pointer to the vtable is set up by the constructor in the normal C++
+way).</p>
+<p>At compilation time, application code includes the header file(s) which
+define(s) the API. At link time, the application includes the DLL's module
+definition file, which allows the address of the DLL function to be accessed
+by specifying its ordinal.</p>
+<p>When the application's executable runs, it loads the DLL at the time it
+is required. The address of the single function exported by the DLL is accessed
+indirectly by specifying its ordinal.</p>
+<p>For a given interface, there may be many DLLs which obey the protocol imposed
+by that interface each of which provides a different implementation.</p>
+<p>A DLL of this type is often referred to as a dynamically loaded DLL.</p>
+<p>The user of a dynamically loaded DLL uses an <codeph>RLibrary</codeph> type
+object to load the DLL. The <codeph>RLibrary</codeph> object encapsulates
+a handle to the DLL and must remain in existence while the DLL is in use;
+typically this is for the life of the object provided by the DLL.</p>
+</conbody></concept>
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