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| <td class="back"><a id="top"></a><a href="s2.3.4.c.html" rel="prev"><< §2.3.4.(c) Actual ambiguity</a></td> |
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| <div class="breadcrumb"><a class="nav" href="s2.html" rel="section">§2 Role Binding</a> > <a class="nav" href="s2.3.html" rel="section">§2.3 Lifting</a> > <a class="nav" href="s2.3.4.html" rel="section">§2.3.4 Binding ambiguities</a></div> |
| <div class="subsect depth4" id="s2.3.4.d"> |
| <h4 class="subsect">§2.3.4.(d) <span class="title">Mismatching role</span><a class="img" href="s2.3.4.d.html" |
| title="PermaLink to (d) 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> |
| </tr> |
| <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> |
| </tr> |
| <tr class="line odd"> |
| <td class="ln">5</td> |
| <td><pre> </pre></td> |
| </tr> |
| <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> |
| </tr> |
| <tr class="line even"> |
| <td class="ln">8</td> |
| <td><pre>}</pre></td> |
| </tr> |
| <tr class="line odd"> |
| <td class="ln">9</td> |
| <td><pre><span class="comment">// plus these calls:</span></pre></td> |
| </tr> |
| <tr class="line even"> |
| <td class="ln">10</td> |
| <td><pre>MyTeam mt = <b>new</b> MyTeam();</pre></td> |
| </tr> |
| <tr class="line odd"> |
| <td class="ln">11</td> |
| <td><pre>MyBase b = <b>new</b> MyBase();</pre></td> |
| </tr> |
| <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> |
| </tr> |
| <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> |
| </tr> |
| <tr class="line even"> |
| <td class="ln">14</td> |
| <td><pre> <span class="comment">// to the expected type SubRoleB.</span></pre></td> |
| </tr> |
| </table> |
| </div> |
| <p>From the second item of <a href="s2.3.4.a.html" title="§2.3.4.(a) Potential ambiguity" |
| class="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">§2 Role Binding</a> > <a class="nav" href="s2.3.html" rel="section">§2.3 Lifting</a> > <a class="nav" href="s2.3.4.html" rel="section">§2.3.4 Binding ambiguities</a></div> |
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