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| <title>OT/J Language Definition v1.3.1</title> |
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| <td class="back"><a id="top"></a><a href="s2.3.d.html" rel="prev"><< §2.3.(d) Lifting of arrays</a></td> |
| <td class="top"><a href="index.html" rel="contents">↑ Table of Contents ↑</a></td> |
| <td class="next"><a href="s2.3.2.html" rel="next">§2.3.2 Declared lifting >></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></div> |
| <div class="sect depth3" id="s2.3.1"> |
| <h3 class="sect">§2.3.1 Implicit role creation<a class="img" href="s2.3.1.html" |
| title="PermaLink to §2.3.1 Implicit role creation"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h3> |
| <p>Lifting tries to reuse existing role objects so that role state persists across |
| lifting and lowering. If no suitable role instance is found during lifting, |
| a new role is created. |
| |
| </p> |
| <div class="subsect depth4" id="s2.3.1.a"> |
| <h4 class="subsect">(a) <span class="title">Reuse of existing role objects</span><a class="img" href="s2.3.1.a.html" |
| title="PermaLink to (a) Reuse of existing role objects"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h4> |
| <p>A role object is considered suitable for reuse during lifting, if |
| these three items are identical: |
| |
| </p> |
| <ol> |
| <li>the given base object</li> |
| <li>the given team object</li> |
| <li>the statically required role type</li> |
| </ol> |
| <p>For the relation between the statically required role type and |
| the actual type of the role object see <a href="s2.3.3.html" title="§2.3.3 Smart lifting" class="sect">"smart lifting" (§2.3.3)</a>. |
| |
| </p> |
| </div> |
| <div class="subsect depth4" id="s2.3.1.b"> |
| <h4 class="subsect">(b) <span class="title">Default lifting constructor</span><a class="img" href="s2.3.1.b.html" |
| title="PermaLink to (b) Default lifting constructor"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h4> |
| <p>Lifting uses a default constructor which takes exactly one argument of the type |
| of the declared base class (after <code>playedBy</code>). |
| By default the compiler generates such a constructor for each bound role. |
| On the other hand, default constructors that take no arguments |
| (as in <a href="http://java.sun.com/docs/books/jls/second_edition/html/classes.doc.html#16823" |
| class="ext">JLS §8.8.7</a>) are never generated for bound roles. |
| <br /> |
| The super-constructor to be invoked by a default lifting constructor |
| depends on whether the role's super class is a bound role or not. |
| |
| </p> |
| <ul> |
| <li>If the super-class is a bound role, the default lifting constructor will invoke the default lifting constructor of the super-class.</li> |
| <li>If the super-class is not a bound role, the default lifting constructor will invoke the normal argumentless default constructor |
| of the super-class. |
| </li> |
| </ul> |
| </div> |
| <div class="subsect depth4" id="s2.3.1.c"> |
| <h4 class="subsect">(c) <span class="title">Custom lifting constructor</span><a class="img" href="s2.3.1.c.html" |
| title="PermaLink to (c) Custom lifting constructor"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h4> |
| <p>If a role class declares a custom constructor with the same signature |
| as the default lifting constructor, this constructor is used during lifting. |
| This custom constructor may pre-assume that the role has been setup |
| properly regarding its base-link and registered in the team's internal map of roles. |
| <br /> |
| If a bound role has an unbound super-class without an argumentless |
| constructor, providing a custom lifting constructor is obligatory, |
| because no legal default lifting constructor can be generated. |
| |
| </p> |
| </div> |
| <div class="subsect depth4" id="s2.3.1.d"> |
| <h4 class="subsect">(d) <span class="title">Fine-tuning role instantiation</span><a class="img" href="s2.3.1.d.html" |
| title="PermaLink to (d) Fine-tuning role instantiation"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h4> |
| <p>If the lifting operation as defined above degrades the program performance, the lifting semantics can be modified per role |
| class |
| by adding the annotation <code>@org.objectteams.Instantiation</code> which requires an argument of type |
| <code>org.objectteams.InstantiationPolicy</code> in order to select between the following behaviors: |
| |
| </p> |
| <dl> |
| <dt>ONDEMAND</dt> |
| <dd>This is the default behavior as defined above.</dd> |
| <dt>ALWAYS</dt> |
| <dd>This strategy avoids maintaining the internal role cache, but instead a fresh role instance is created for each lifting request. |
| This may increase the number of role instances but cuts the costs of accessing the cache, which could otherwise become |
| |
| expensive if a cache grows large. As a result of this strategy role state can no longer be shared |
| over time, thus it is discouraged to define fields in a role with this strategy. Also, comparing roles could lead |
| to |
| unexpected results. Therefor, roles with this strategy should implement custom <code>equals</code> and <code>hashCode</code> |
| methods, which should simply delegate to the base instance (using callout <a href="s3.html" title="§3 Callout Binding" class="sect">§3</a>). |
| </dd> |
| <dt>NEVER</dt> |
| <dd>Roles with this instantiation policy are never instantiated by lifting. |
| Such roles cannot define non-static fields. |
| Otherwise this optimization is fully transparent, specifically callout bindings will refer to the correct base instance.<br /> |
| As of version 2.0 the OT/J compiler does not implement this strategy. |
| </dd> |
| <dt>SINGLETON</dt> |
| <dd>Roles declaring this strategy will be instantiated at most once per team. Subsequent lifting requests in the same team |
| will always answer the same role instance. Such roles may receive triggers from callin bindings, but cannot define |
| callout bindings.<br /> |
| As of version 2.0 the OT/J compiler does not implement this strategy. |
| </dd> |
| </dl> |
| </div> |
| </div> |
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| <td class="back"><a href="s2.3.d.html" rel="prev"><< §2.3.(d) Lifting of arrays</a></td> |
| <td class="top"><a href="index.html" rel="contents">↑ Table of Contents ↑</a></td> |
| <td class="next"><a href="s2.3.2.html" rel="next">§2.3.2 Declared lifting >></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></div> |
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| OT/J version 1.3.1 — last modified: 2013-05-28 |
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