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<td class="back"><a id="top"></a><a href="s2.3.4.c.html" rel="prev">&lt;&lt;&nbsp;&sect;2.3.4.(c)&nbsp;Actual ambiguity</a></td>
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<div class="breadcrumb"><a class="nav" href="s2.html" rel="section">&sect;2&nbsp;Role Binding</a>&nbsp;&gt;&nbsp;<a class="nav" href="s2.3.html" rel="section">&sect;2.3&nbsp;Lifting</a>&nbsp;&gt;&nbsp;<a class="nav" href="s2.3.4.html" rel="section">&sect;2.3.4&nbsp;Binding ambiguities</a></div>
<div class="subsect depth4" id="s2.3.4.d">
<h4 class="subsect">&sect;2.3.4.(d)&nbsp;<span class="title">Mismatching role</span><a class="img" href="s2.3.4.d.html"
title="PermaLink to (d)&nbsp;Mismatching role"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png"
alt="" /></a></h4>
<p>In cases of potential ambiguity another runtime error may occur:
a <strong>mismatching role</strong> is encountered when a role is found
in the cache, which is not conform to the required type.
This happens, if the base object has previously been lifted
to a type that is incompatible with the currently requested type.
</p>
<div class="note">
<h5>Effect:</h5>
This is reported by throwing a <code>org.objectteams.WrongRoleException</code>.
</div>
<h5 class="listing">Example code (Mismatching Role):</h5>
<div class="listing example frame">
<table class="listing">
<tr class="line odd">
<td class="ln">1</td>
<td><pre><b>team</b> <b>class</b> MyTeam {</pre></td>
</tr>
<tr class="line even">
<td class="ln">2</td>
<td><pre> <b>public</b> <b>class</b> SuperRole <b>playedBy</b> MyBase {...}</pre></td>
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<tr class="line odd">
<td class="ln">3</td>
<td><pre> <b>public</b> <b>class</b> SubRoleA <b>extends</b> SuperRole {...}</pre></td>
</tr>
<tr class="line even">
<td class="ln">4</td>
<td><pre> <b>public</b> <b>class</b> SubRoleB <b>extends</b> SuperRole {...}</pre></td>
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<tr class="line odd">
<td class="ln">5</td>
<td><pre> </pre></td>
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<tr class="line even">
<td class="ln">6</td>
<td><pre> <b>public</b> <b>void</b> useRoleA(MyBase <b>as</b> SubRoleA r) {...}</pre></td>
</tr>
<tr class="line odd">
<td class="ln">7</td>
<td><pre> <b>public</b> <b>void</b> useRoleB(MyBase <b>as</b> SubRoleB r) {...}</pre></td>
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<td class="ln">8</td>
<td><pre>}</pre></td>
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<tr class="line odd">
<td class="ln">9</td>
<td><pre><span class="comment">// plus these calls:</span></pre></td>
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<td class="ln">10</td>
<td><pre>MyTeam mt = <b>new</b> MyTeam();</pre></td>
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<tr class="line odd">
<td class="ln">11</td>
<td><pre>MyBase b = <b>new</b> MyBase();</pre></td>
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<tr class="line even">
<td class="ln">12</td>
<td><pre>mt.useRoleA(b); <span class="comment">// creates a SubRoleA for b</span></pre></td>
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<tr class="line odd">
<td class="ln">13</td>
<td><pre>mt.useRoleB(b); <span class="comment">// finds the SubRoleA which is not compatible</span></pre></td>
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<tr class="line even">
<td class="ln">14</td>
<td><pre> <span class="comment">// to the expected type SubRoleB.</span></pre></td>
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<p>From the second item of <a href="s2.3.4.a.html" title="&sect;2.3.4.(a)&nbsp;Potential ambiguity"
class="sect">&sect;2.3.4.(a)</a> follows, that for binding ambiguities different
role hierarchies are analyzed in isolation.
For this analysis only those role classes are considered that are bound to a
base class (directly using <code>playedBy</code> or by inheriting this relation
from another role class).
I.e., two role classes that have no common bound super role will never cause
any ambiguity.
</p>
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<div class="breadcrumb"><a class="nav" href="s2.html" rel="section">&sect;2&nbsp;Role Binding</a>&nbsp;&gt;&nbsp;<a class="nav" href="s2.3.html" rel="section">&sect;2.3&nbsp;Lifting</a>&nbsp;&gt;&nbsp;<a class="nav" href="s2.3.4.html" rel="section">&sect;2.3.4&nbsp;Binding ambiguities</a></div>
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OT/J version 1.3 &mdash; last modified: 2010-06-08
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