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| <td class="top"><a href="index.html" rel="contents">↑ Table of Contents ↑</a></td> |
| <td class="next"><a href="s2.4.2.html" rel="next">§2.4.2 Role creation via a regular constructor >></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="s2.4.1"> |
| <h3 class="sect">§2.4.1 Role creation via a lifting constructor<a class="img" href="s2.4.1.html" |
| title="PermaLink to §2.4.1 Role creation via a lifting constructor"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
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| <p>Lifting uses the default constructor for roles (see <a href="s2.3.1.html" title="§2.3.1 Implicit role creation" |
| class="sect">§2.3.1</a>). |
| This constructor can be invoked from client code, if the following rules are respected. |
| |
| </p> |
| <div class="subsect depth4" id="s2.4.1.a"> |
| <h4 class="subsect">(a) <span class="title">Team context</span><a class="img" href="s2.4.1.a.html" title="PermaLink to (a) Team context"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h4> |
| <p>The lifting constructor can be used only within the enclosing team of |
| the role to be instantiated. Thus, qualified allocation expressions |
| (<code>someTeam.new SomeRole(..)</code>) may never use the lifting constructor. |
| |
| </p> |
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| <div class="subsect depth4" id="s2.4.1.b"> |
| <h4 class="subsect">(b) <span class="title">Fresh base object</span><a class="img" href="s2.4.1.b.html" |
| title="PermaLink to (b) Fresh base object"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h4> |
| <p>If the argument to a lifting constructor invocation is a <code>new</code> |
| expression, creating a fresh base object, the use of the lifting constructor |
| is safe. Otherwise the rules of (c) below apply. |
| |
| </p> |
| </div> |
| <div class="subsect depth4" id="s2.4.1.c"> |
| <h4 class="subsect">(c) <span class="title">Duplicate role runtime check</span><a class="img" href="s2.4.1.c.html" |
| title="PermaLink to (c) Duplicate role runtime check"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png" |
| alt="" /></a></h4> |
| <p>If it cannot be syntactically derived, that the argument to a lifting |
| constructor is a freshly created base object (b), a compile time warning will |
| signal that an additional runtime check is needed: It must be prevented that |
| a new role is created for a base object, which already has a role of the |
| required type in the given team. It is not possible to replace an existing |
| role by use of the lifting constructor. At runtime, any attempt to do so |
| will cause a <code>org.objectteams.DuplicateRoleException</code> to be thrown. |
| This exception can only occur in situations where the mentioned compile |
| time warning had been issued. |
| <br /><a href="s6.1.html" title="§6.1 Reflection" class="sect">§6.1</a> will introduce reflective functions |
| which can be used to manually prevent errors like a duplicate role. |
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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> |
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