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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="s2.4.1.html" rel="prev"><< §2.4.1 Role creation via a lifting constructor</a></td> |
| <td class="top"><a href="index.html" rel="contents">↑ Table of Contents ↑</a></td> |
| <td class="next"><a href="s2.4.3.html" rel="next">§2.4.3 Role creation in the presence of smart 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="s2.4.html" rel="section">§2.4 Explicit role creation</a></div> |
| <div class="sect depth3" id="s2.4.2"> |
| <h3 class="sect">§2.4.2 Role creation via a regular constructor<a class="img" href="s2.4.2.html" |
| title="PermaLink to §2.4.2 Role creation via a regular constructor"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h3> |
| <p>Roles may also be created explicitly using a custom constructor with arbitrary signature |
| other than the signature of the lifting constructor.<br /> |
| Within role constructors, four kinds of self-calls are possible: |
| |
| </p> |
| <dl> |
| <dt><code>base(..)</code></dt> |
| <dd>A constructor of the corresponding base class (<a href="sA.html#sA.5.3" title="§A.5.3 BaseCall" class="sect">§A.5.3</a>(c)), |
| <span class="underline">unless</span> the role is involved in base class circularity (<a href="s2.1.2.b.html" title="§2.1.2.(b) Cycles" class="sect">§2.1.2.(b)</a>), |
| in which case a base constructor call is illegal. |
| </dd> |
| <dt><code>this(..)</code></dt> |
| <dd>Another constructor of the same class.</dd> |
| <dt><code>super(..)</code></dt> |
| <dd>A constructor of the super-class (normal <code>extends</code>), <span class="underline">unless</span> the super-class is bound to a different base class, in which case calling <code>super(..)</code> is not legal. |
| </dd> |
| <dt><code>tsuper(..)</code></dt> |
| <dd>A constructor of the corresponding role of the super-team (<a href="sA.html#sA.5.4" title="§A.5.4 TSuperCall" class="sect">§A.5.4</a>(e)). Also see the constraint in <a href="s1.3.2.c.html" |
| title="§1.3.2.(c) Constructors and overridden 'extends' " |
| class="sect">§1.3.2.(c)</a>. |
| </dd> |
| </dl> |
| <div class="subsect depth4" id="s2.4.2.a"> |
| <h4 class="subsect">(a) <span class="title">Unbound roles</span><a class="img" href="s2.4.2.a.html" title="PermaLink to (a) Unbound roles"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h4> |
| <p>Each constructor of a role that is <strong>not bound</strong> to a base class must use |
| one of <code>this(..)</code>, <code>super(..)</code> or <code>tsuper(..)</code>. |
| |
| </p> |
| </div> |
| <div class="subsect depth4" id="s2.4.2.b"> |
| <h4 class="subsect">(b) <span class="title">Bound roles</span><a class="img" href="s2.4.2.b.html" title="PermaLink to (b) Bound roles"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h4> |
| <p>Each constructor of a <strong>bound role</strong> must directly or indirectly invoke either |
| a <code>base(..)</code> constructor or a lifting constructor (see <a href="s2.3.1.html" title="§2.3.1 Implicit role creation" |
| class="sect">§2.3.1</a>). |
| Indirect calls to the base constructor or lifting constructor may use any of <code>this(..)</code>, <code>super(..)</code> |
| or <code>tsuper(..)</code>, which simply delegates the obligation to the called constructor. |
| <br /> |
| If a constructor referenced by <code>base(..)</code> is not visible according to the |
| regular rules of Java, it may still be called using <b>decapsulation</b> (see |
| also <a href="s3.4.html" title="§3.4 Overriding access restrictions" |
| class="sect">§3.4</a>, <a href="s2.1.2.c.html" title="§2.1.2.(c) Base class decapsulation" |
| class="sect">§2.1.2.(c)</a>). |
| <br /> |
| Note, that if the super or tsuper role is not bound, delegating the obligation to that unbound role will not work. |
| |
| </p> |
| </div> |
| <div class="subsect depth4" id="s2.4.2.c"> |
| <h4 class="subsect">(c) <span class="title">Super-call for bound roles</span><a class="img" href="s2.4.2.c.html" |
| title="PermaLink to (c) Super-call for bound roles"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h4> |
| <p>Instead of or prior to calling <code>base(..)</code> a constructor of a bound role explicitly or implicitly calls a super constructor. |
| Which constructor is applicable depends on the super role and its <code>playedBy</code> clause. |
| |
| </p> |
| <ul> |
| <li>If the super role is bound to the same base class as the current role is, |
| |
| <ul> |
| <li>not writing a super-call causes the lifting constructor of the super role to be invoked.</li> |
| <li>explicitly calling a super constructor requires the super constructor to <i>either</i><ol> |
| <li>create a role instance using a base constructor call (directly or indirectly), <i>or</i></li> |
| <li>be a lifting constructor receiving a base instance, which the current role must provide as the argument.</li> |
| </ol> |
| </li> |
| </ul> |
| </li> |
| <li>If the super role is bound but the current role refines the <code>playedBy</code> |
| relationship (cf. <a href="s2.1.c.html" title="§2.1.(c) Covariant refinement" |
| class="sect">§2.1.(c)</a>), |
| |
| <ul> |
| <li>a lifting constructor must be called explicitly passing a base object as the argument.</li> |
| </ul> |
| </li> |
| <li>If the role has an explicit or implicit super role which is unbound the constructor may optionally |
| call a super constructor (using <code>super(..)</code> or <code>tsuper(..)</code>) prior to calling |
| <code>base(..)</code>. Otherwise the default constructor is implicitly invoked. |
| |
| </li> |
| </ul> |
| <p>When invoking a lifting constructor of a super role the base object can optionally be obtained by using a base constructor |
| call as an expression: |
| |
| </p> |
| <div class="listing plain"><pre>super(base(<i><args></i>));</pre></div> |
| </div> |
| <p>The language system evaluates the base constructor by creating an |
| instance of the appropriate base class using a constructor with matching |
| signature. Also the internal links are setup that are needed for accessing the |
| base object from the role and for lifting the base object to the new role |
| in the future. |
| |
| </p> |
| <p>The syntax for base constructors follows the rule that role implementations |
| never directly refer to any names of base classes or their features. |
| |
| </p> |
| </div> |
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| <td class="back"><a href="s2.4.1.html" rel="prev"><< §2.4.1 Role creation via a lifting constructor</a></td> |
| <td class="top"><a href="index.html" rel="contents">↑ Table of Contents ↑</a></td> |
| <td class="next"><a href="s2.4.3.html" rel="next">§2.4.3 Role creation in the presence of smart lifting >></a></td> |
| </tr> |
| </table> |
| <div class="breadcrumb"><a class="nav" href="s2.html" rel="section">§2 Role Binding</a> > <a class="nav" href="s2.4.html" rel="section">§2.4 Explicit role creation</a></div> |
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