| <!DOCTYPE html |
| PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "../xhtml1-strict.dtd"> |
| <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> |
| <head> |
| <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> |
| <link rel="stylesheet" type="text/css" href="../css/ot.css" /> |
| <link rel="stylesheet" type="text/css" href="../css/otjld.css" /> |
| <title>OT/J Language Definition v1.3</title> |
| </head> |
| <body class="otdt"> |
| <div id="content"> |
| <table class="nav"> |
| <tr> |
| <td class="back"><a id="top"></a><a href="s2.3.3.html" rel="prev"><< §2.3.3 Smart lifting</a></td> |
| <td class="top"><a href="index.html" rel="contents">↑ Table of Contents ↑</a></td> |
| <td class="next"></td> |
| </tr> |
| </table> |
| <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></div> |
| <div class="sect depth3" id="s2.3.4"> |
| <h3 class="sect">§2.3.4 Binding ambiguities<a class="img" href="s2.3.4.html" |
| title="PermaLink to §2.3.4 Binding ambiguities"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h3> |
| <p>While all examples so far have only shown 1-to-1 class bindings, |
| several cases of multiple bindings are allowable. Ambiguities may be |
| detected at compile time and/or at runtime. |
| |
| </p> |
| <div class="subsect depth4" id="s2.3.4.a"> |
| <h4 class="subsect">(a) <span class="title">Potential ambiguity</span><a class="img" href="s2.3.4.a.html" |
| title="PermaLink to (a) Potential ambiguity"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h4> |
| <p>A <strong>potential ambiguity</strong> is given, |
| if two role classes <code>R1</code> and <code>R2</code> |
| exist such that |
| |
| </p> |
| <ul> |
| <li><code>R1</code> and <code>R2</code> are played by the |
| same base class <code>B</code>, and |
| </li> |
| <li><code>R1</code> and <code>R2</code> have a common |
| super role <code>R0</code>, |
| which is also bound to a base class <code>B0</code>, and |
| </li> |
| <li>neither role class <code>R1</code> nor |
| <code>R2</code> is a (indirect) sub-class of the other. |
| </li> |
| </ul> |
| <div class="note"> |
| <h5>Note:</h5> |
| According to <a href="s2.1.c.html" title="§2.1.(c) Covariant refinement" |
| class="sect">§2.1.(c)</a>, if <code>B</code> is distinct from <code>B0</code> |
| it has to be a sub-class of <code>B0</code>. |
| |
| </div> |
| <div class="note"> |
| <h5>Effect:</h5> |
| In this case the compiler issues a warning, stating that the <code>B</code><em> may not be liftable,</em> because both role classes <code>R1</code> |
| and <code>R2</code> are candidates and there is no reason to prefer one over the other. |
| <br /><strong>If no potential ambiguity is detected, lifting will always be unambiguous.</strong></div> |
| <p>In the above situation, trying to lift an instance of type <code>B</code> to the role type |
| <code>R0</code> is an <strong>illegal lifting request</strong>. If <code>R0</code> is bound |
| to the same base class <code>B</code> as its sub-roles <code>R1</code> and <code>R2</code> are, |
| role <code>R0</code> is <strong>unliftable</strong>, meaning that no instance of <code>R0</code> |
| can ever by obtained by lifting. |
| |
| </p> |
| <h5 class="listing">Example code (Potential Ambiguity):</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> |
| </table> |
| </div> |
| </div> |
| <div class="subsect depth4" id="s2.3.4.b"> |
| <h4 class="subsect">(b) <span class="title">Definite ambiguity</span><a class="img" href="s2.3.4.b.html" |
| title="PermaLink to (b) Definite ambiguity"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h4> |
| <p>A <strong>definite ambiguity</strong> is given if |
| |
| </p> |
| <ul> |
| <li>the situation of potential ambiguity according to (a) |
| above is given and |
| </li> |
| <li>lifting is requested (either by method binding or explicitly |
| (<a href="s2.3.2.html" title="§2.3.2 Declared lifting" class="sect">§2.3.2</a>)) from the shared base class <code>B</code> to any role |
| class <code>R0</code> that is a common super role for <code>R1</code> and <code>R2</code>. |
| </li> |
| </ul> |
| <div class="note"> |
| <h5>Effect:</h5> |
| Definite ambiguity is a compile time error. |
| |
| </div> |
| <h5 class="listing">Example code (Definite Ambiguity):</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 <b>playedBy</b> SubBase {...}</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 <b>playedBy</b> SubBase {...}</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> useSuperRole(SubBase <b>as</b> SuperRole r) {...}</pre></td> |
| </tr> |
| <tr class="line odd"> |
| <td class="ln">7</td> |
| <td><pre>}</pre></td> |
| </tr> |
| </table> |
| </div> |
| </div> |
| <div class="subsect depth4" id="s2.3.4.c"> |
| <h4 class="subsect">(c) <span class="title">Actual ambiguity</span><a class="img" href="s2.3.4.c.html" |
| title="PermaLink to (c) Actual ambiguity"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h4> |
| <p>At runtime <strong>actual ambiguity</strong> may occur if for the |
| <em>dynamic type</em> of a base to be lifted the conditions of (b) |
| above hold accordingly. Actual ambiguity is only possible in cases |
| reported by the compiler as potential ambiguity. |
| |
| </p> |
| <div class="note"> |
| <h5>Effect:</h5> |
| An actual ambiguity is reported at runtime by throwing a |
| <code>org.objectteams.LiftingFailedException</code>. |
| |
| </div> |
| <h5 class="listing">Example code (Actual Ambiguity):</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 <b>playedBy</b> SubBase {...}</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 <b>playedBy</b> SubBase {...}</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> useSuperRole(MyBase <b>as</b> SuperRole r) {...}</pre></td> |
| </tr> |
| <tr class="line odd"> |
| <td class="ln">7</td> |
| <td><pre>}</pre></td> |
| </tr> |
| <tr class="line even"> |
| <td class="ln">8</td> |
| <td><pre><span class="comment">// plus these calls:</span></pre></td> |
| </tr> |
| <tr class="line odd"> |
| <td class="ln">9</td> |
| <td><pre>MyTeam mt = <b>new</b> MyTeam();</pre></td> |
| </tr> |
| <tr class="line even"> |
| <td class="ln">10</td> |
| <td><pre>mt.useSuperRole(<b>new</b> SubBase());</pre></td> |
| </tr> |
| </table> |
| </div> |
| </div> |
| <div class="subsect depth4" id="s2.3.4.d"> |
| <h4 class="subsect">(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" 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> |
| </div> |
| </div> |
| <table class="nav"> |
| <tr> |
| <td class="back"><a href="s2.3.3.html" rel="prev"><< §2.3.3 Smart lifting</a></td> |
| <td class="top"><a href="index.html" rel="contents">↑ Table of Contents ↑</a></td> |
| <td class="next"></td> |
| </tr> |
| </table> |
| <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></div> |
| </div> |
| <div id="footer"> |
| <hr /><a class="w3c img" href="http://jigsaw.w3.org/css-validator/check/referer" |
| shape="rect"><img src="../images/valid-css2-blue.png" alt="Valid CSS!" height="31" width="88" /></a><a class="w3c img" href="http://validator.w3.org/check?uri=referer" shape="rect"><img src="../images/valid-xhtml10-blue.png" alt="Valid XHTML 1.0 Strict" height="31" |
| width="88" /></a><address>© Stephan Herrmann, Christine Hundt, Marco Mosconi</address> |
| OT/J version 1.3 — last modified: 2010-06-08 |
| </div> |
| </body> |
| </html> |