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<a name="Value-Classes-vs_002e-Handle-Classes"></a>
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<a name="Value-Classes-vs_002e-Handle-Classes-1"></a>
<h4 class="subsection">34.6.5 Value Classes vs. Handle Classes</h4>
<p>There are two intrinsically different types of <code>classdef</code> classes, whose
major difference is the behavior regarding variable assignment. The first type
are <b>value classes</b>:
</p>
<div class="example">
<pre class="example">classdef value_class
properties
prop1
endproperties
methods
function obj = set_prop1 (obj, val)
obj.prop1 = val;
endfunction
endmethods
endclassdef
</pre></div>
<p>Assigning an object of that class to another variable essentially creates a new
object:
</p>
<div class="example">
<pre class="example">>> a = value_class ();
>> a.prop1 = 1;
>> b = a;
>> b.prop1 = 2;
>> b.prop1
⇒ ans = 2
>> a.prop1
⇒ ans = 1
</pre></div>
<p>But that also means that you might have to assign the output of a method that
changes properties back to the object manually:
</p>
<div class="example">
<pre class="example">>> a = value_class ();
>> a.prop1 = 1;
>> a.set_prop1 (3);
⇒ ans =
<object value_class>
>> ans.prop1
⇒ ans = 3
>> a.prop1
⇒ ans = 1
</pre></div>
<p>The second type are <b>handle classes</b>. Those classes have to be derived from
the abstract <code>handle</code> class:
</p>
<div class="example">
<pre class="example">classdef handle_class < handle
properties
prop1
endproperties
methods
function set_prop1 (obj, val)
obj.prop1 = val;
endfunction
endmethods
endclassdef
</pre></div>
<p>In the following example, the variables <code>a</code> and <code>b</code> refer to the
very same object of class <code>handle_class</code>:
</p>
<div class="example">
<pre class="example">>> a = handle_class ();
>> a.prop1 = 1;
>> b = a;
>> b.prop1 = 2;
>> b.prop1
⇒ ans = 2
>> a.prop1
⇒ ans = 2
</pre></div>
<p>Object properties that are modified by a method of an handle class are changed
persistently:
</p>
<div class="example">
<pre class="example">>> a.set_prop1 (3);
>> a.prop1
⇒ ans = 3
</pre></div>
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