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<b>Data Structures and Algorithms 
with Object-Oriented Design Patterns in C++</b><br>
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<H3><A NAME="SECTION006221000000000000000">Implementation</A></H3>
<P>
Only three functions need to be implemented to
complete the definition of the <tt>Object</tt> class.
These are shown in Program&nbsp;<A HREF="page112.html#progobject1c" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page112.html#progobject1c"><IMG  ALIGN=BOTTOM ALT="gif" SRC="cross_ref_motif.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/icons/cross_ref_motif.gif"></A>.
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<P><A NAME="5451">&#160;</A><A NAME="progobject1c">&#160;</A> <IMG WIDTH=575 HEIGHT=333 ALIGN=BOTTOM ALT="program4614" SRC="img684.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img684.gif"  ><BR>
<STRONG>Program:</STRONG> <tt>Object</tt> Class Member Function Definitions<BR>
<P>
<P>
The <tt>Object</tt> class destructor is trivial.
Since there are no member variables,
nothing remains to be cleaned up.
It is necessary to define the destructor in any event.
As explained above, the destructor needs to be <tt>virtual</tt>
and because in C++ there is no such thing as a pure virtual destructor.
<P>
The implementation of the <tt>IsNull</tt> member function is trivial.
It simply returns the Boolean value <tt>false</tt>.
<P>
The <tt>Compare</tt> member function makes use of
<em>run-time type information</em><A NAME=4632>&#160;</A>
to ensure that the <tt>CompareTo</tt> member function
is only invoked for objects which are of the same class.
For objects which are not instances of the same class,
the <tt>before</tt> function is used to order those objects
based on their types.
The C++ run-time library provides an implementation for the <tt>before</tt>
function which returns true if the left hand type
precedes the right hand type in the implementation's collation order.
<P>
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