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<td class="back"><a id="top"></a><a href="s2.4.2.html" rel="prev">&lt;&lt;&nbsp;&sect;2.4.2&nbsp;Role creation via a regular constructor</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="s2.4.html" rel="section">&sect;2.4&nbsp;Explicit role creation</a></div>
<div class="sect depth3" id="s2.4.3">
<h3 class="sect">&sect;2.4.3&nbsp;Role creation in the presence of smart lifting<a class="img" href="s2.4.3.html"
title="PermaLink to &sect;2.4.3&nbsp;Role creation in the presence of smart lifting"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png"
alt="" /></a></h3>
<p>Explicitly instantiating a role <code>R1</code> bound to a base <code>B</code> where smart lifting of <code>B</code> to <code>R1</code> would actually
provide a subrole <code>R2</code> is dangerous: Instantiation enters the <code>R1</code> into the team's internal cache. If at any time later lifting
this <code>B</code> to <code>R2</code> is requested, which is a legal request, the runtime system will answer by throwing a <code>org.objectteams.WrongRoleException</code>
because it finds the <code>R1</code> instead of the required <code>R2</code>.
For this reason, in this specific situation the explicit instantiation <code>new R1(..)</code> will be flagged by a warning.
The problem can be avoided by using <code>R2</code> in the instantiation expression.
</p>
<h5 class="listing">Example code (WrongRoleException):</h5>
<div class="listing example frame">
<table class="listing">
<tr class="line odd">
<td class="ln">1</td>
<td><pre><b>public</b> <b>class</b> B { <b>void</b> bm() {} }</pre></td>
</tr>
<tr class="line even">
<td class="ln">2</td>
<td><pre><b>public</b> <b>team</b> <b>class</b> T {</pre></td>
</tr>
<tr class="line odd">
<td class="ln">3</td>
<td><pre> <b>protected</b> <b>class</b> R1 <b>playedBy</b> B {...}</pre></td>
</tr>
<tr class="line even">
<td class="ln">4</td>
<td><pre> <b>protected</b> <b>class</b> R2 <b>extends</b> R1 { <span class="comment">// inherits the binding to B</span></pre></td>
</tr>
<tr class="line odd">
<td class="ln">5</td>
<td><pre> <b>void</b> rm() { <span class="comment">/* body omitted */</span> }</pre></td>
</tr>
<tr class="line even">
<td class="ln">6</td>
<td><pre> }</pre></td>
</tr>
<tr class="line odd">
<td class="ln">7</td>
<td><pre> <b>public</b> B getDecoratedB() {</pre></td>
</tr>
<tr class="line even">
<td class="ln">8</td>
<td><pre> <b>return</b> <em><b>new</b> R1</em>(<b>new</b> B()); <span class="comment">// <span class="error">compile-time warning!</span></span></pre></td>
</tr>
<tr class="line odd">
<td class="ln">9</td>
<td><pre> }</pre></td>
</tr>
<tr class="line even">
<td class="ln">10</td>
<td><pre> <b>public</b> <b>void</b> requestLifting(B <b>as</b> R2 r) {}</pre></td>
</tr>
<tr class="line odd">
<td class="ln">11</td>
<td><pre>}</pre></td>
</tr>
<tr class="line even">
<td class="ln">12</td>
<td><pre><span class="comment">// plus these calls:</span></pre></td>
</tr>
<tr class="line odd">
<td class="ln">13</td>
<td><pre>T t = <b>new</b> T();</pre></td>
</tr>
<tr class="line even">
<td class="ln">14</td>
<td><pre>B b = t.getDecoratedB(); <span class="comment">// creates an R1 for b</span></pre></td>
</tr>
<tr class="line odd">
<td class="ln">15</td>
<td><pre>t.requestLifting(b); <span class="comment">// =&gt; <span class="error"><code>org.objectteams.WrongRoleException!</code></span></span></pre></td>
</tr>
</table>
</div>
<div class="codecomment">
<ul>
<li>A note on line 8: this line passes a fresh instance of <code>B</code> to the lifting constructor of <code>R1</code>
(see <a href="s2.4.1.b.html" title="&sect;2.4.1.(b)&nbsp;Fresh base object"
class="sect">&sect;2.4.1.(b)</a>). In order to return this <code>B</code> instance lowering is implicitly used for the return statement.
</li>
<li>When line 15 is executed, a lifting of <code>b</code> to <code>R2</code> is requested but due to line 8 an <code>R1</code> is found in the internal cache.
</li>
</ul>
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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="s2.4.html" rel="section">&sect;2.4&nbsp;Explicit role creation</a></div>
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