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<TITLE>Implementation</TITLE>
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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="SECTION0062111000000000000000">Implementation</A></H3>
<P>
Two constructors and the destructor are defined in Program <A HREF="page126.html#progassoc1c" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page126.html#progassoc1c"><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>.
The first constructor takes as its lone argument
a reference to an <tt>Object</tt>.
It makes its <tt>key</tt> member variable point at the specified object
and sets the <tt>value</tt> pointer to zero.
The second constructor takes two arguments--both of them a reference to an <tt>Object</tt>.
The <tt>key</tt> and <tt>value</tt> member variables are made
to point at the corresponding objects.
<P>
<P><A NAME="5555"> </A><A NAME="progassoc1c"> </A> <IMG WIDTH=575 HEIGHT=353 ALIGN=BOTTOM ALT="program5258" SRC="img700.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img700.gif" ><BR>
<STRONG>Program:</STRONG> <tt>Association</tt> Class Constructor and Destructor<BR>
<P>
<P>
The destructor follows the general framework for the destructor
of a class derived from <tt>Ownership</tt>.
If the association is the owner of the contained key and value,
then those objects must be deleted by the destructor.
<P>
The remaining member functions of the <tt>Association</tt> class
are defined in Program <A HREF="page126.html#progassoc2c" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page126.html#progassoc2c"><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>.
The first two, <tt>Key</tt> and <tt>Value</tt>, are member variable accessors.
The former returns a reference to the key object
obtained by dereferencing the <tt>key</tt> member variable;
the latter, a reference to the value object
obtained by dereferencing the <tt>value</tt> member variable.
<P>
<P><A NAME="5558"> </A><A NAME="progassoc2c"> </A> <IMG WIDTH=575 HEIGHT=486 ALIGN=BOTTOM ALT="program5275" SRC="img701.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img701.gif" ><BR>
<STRONG>Program:</STRONG> <tt>Association</tt> Class Member Functions<BR>
<P>
<P>
The <tt>CompareTo</tt> function is one place where
an association distinguishes between the key and the value.
The <tt>CompareTo</tt> function only operates on the key.
The <tt>CompareTo</tt> function takes as its lone argument
a <tt>const</tt> reference to <tt>Object</tt>.
It uses the <tt>dynamiccast</tt><A NAME=5295> </A>
operator to convert the argument to an <tt>Association</tt>.
The result of the comparison is based solely
on the keys of the objects--the values have no rôle in the comparison.
<P>
Finally, the purpose of the <tt>Put</tt> member function
is to print out a representation of the association.
The implementation is trivial and needs no further explanation.
<P>
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