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<b>Data Structures and Algorithms
with Object-Oriented Design Patterns in C++</b><br>
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<H2><A NAME="SECTION0018330000000000000000">Accessors and Mutators</A></H2>
<P>
An <em>accessor</em><A NAME=57334> </A> is a member function that
accesses the contents of an object but does not modify that object.
In the simplest case,
an accessor just returns the value of one of the member variables.
In general,
an accessor performs some computation using the member variables
as long as that computation does not modify any of the member variables.
<P>
Program <A HREF="page603.html#progcomplex2c" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page603.html#progcomplex2c"><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> defines the five accessor member functions
of the <tt>Complex</tt> class--<tt>Real</tt>, <tt>Imag</tt>, <tt>R</tt>, <tt>Theta</tt> and <tt>Put</tt>.
The fact that these functions are accessors is indicated by the
<tt>const</tt> keyword at the end of the function declarator.
The <tt>const</tt> signifies that this member function is not permitted
to modify the object on which it operates.
In fact, the C++ compiler will not allow any operations
that could modify any of the member variables of the object.
<P>
<P><A NAME="57741"> </A><A NAME="progcomplex2c"> </A> <IMG WIDTH=575 HEIGHT=279 ALIGN=BOTTOM ALT="program57344" SRC="img2603.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img2603.gif" ><BR>
<STRONG>Program:</STRONG> <tt>Complex</tt> Class Accessors<BR>
<P>
<P>
By defining suitable accessors,
it is possible to hide the implementation of the class from the user
of that class.
Consider the following statements:
<PRE>cout << c.real << endl;
cout << c.Real() << endl;</PRE>
The first statement depends on the implementation of the <tt>Complex</tt> class.
If we change the implementation of the class from
the one given (which uses rectangular coordinates)
to one that uses polar coordinates,
then the first statement above must also be changed.
On the other hand,
the second statement does not need to be modified,
provided we reimplement the <tt>Real</tt> member function
when we switch to polar coordinates.
<P>
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