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                <td class="back"><a id="top"></a><a href="s6.2.d.html" rel="prev">&lt;&lt;&nbsp;&sect;6.2.(d)&nbsp;Exceptions</a></td>
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          <div class="breadcrumb"><a class="nav" href="s6.html" rel="section">&sect;6&nbsp;Object Teams API</a>&nbsp;&gt;&nbsp;<a class="nav" href="s6.2.html" rel="section">&sect;6.2&nbsp;Other API Elements</a></div>
          <div class="subsect depth3" id="s6.2.e">
             <h4 class="subsect">&sect;6.2.(e)&nbsp;<span class="title">Role migration</span><a class="img" href="s6.2.e.html" title="PermaLink to (e)&nbsp;Role migration"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png"
                        alt="" /></a></h4>
             <p>The following interfaces can be used to enable role migration:</p>
             <dl>
                <dt><code>IBaseMigratable</code></dt>
                <dd>This interface declares a method
                   <div class="listing plain"><pre>
     <code>&lt;B&gt; <b>void</b> migrateToBase(B otherBase)</code> </pre></div>
                   					and instructs the compiler to generate an implementation of this method
                   					for any bound role declaring <code>IBaseMigratable</code> as its super-interface.<br />
                   					The effect of calling <code>migrateToBase</code> on a role instance is to re-bind this role to a new base instance.
                   					The base instance must be compatible to the role's base class (in order to avoid problems during lifting the
                   					compiler may require the base to be of the exact type of the role's base class).
                   					Passing <code>null</code> to this method causes an <code>NullPointerException</code> to be thrown.
                </dd>
                <dt><code>ITeamMigratable</code></dt>
                <dd>This interface declares a method
                   <div class="listing plain"><pre>
     <code>&lt;R&gt; R&lt;@otherTeam&gt; migrateToTeam(<b>final</b> ITeam otherTeam)</code></pre></div>
                   					and instructs the compiler to
                   					generate an implementation of this method for any role declaring <code>ITeamMigratable</code> as its super-interface.<br />
                   					The effect of calling <code>migrateToTeam</code> on a role instance is to re-bind this role to become a contained part of a new team instance.
                   					The team instance must be of the exact type of the role's enclosing team.
                   					Passing <code>null</code> to this method causes a <code>NullPointerException</code> to be thrown.<br /><div class="note">
                      <h5>Caveat:</h5>
                      					This method intentionally breaks the rules of family polymorphism: any reference <code>R&lt;@previousTeam&gt; r</code>
                      					which was established before migration will incorrectly imply that the role's enclosing team still is <code>previousTeam</code>,
                      					which is no longer true after migration.
                      					While this does not effect any method lookup (which is still safe), further assumptions based on a role's dependent type
                      					are invalidated by team migration. The same holds for references from the migrating role to any sibling role instances.<br />
                      					If the rules of family polymorphism should be maintained one should just refrain from declaring <code>ITeamMigratable</code>
                      					as a role's super-interface.
                   </div>
                </dd>
             </dl>
             <p>For both methods the signature declared in the interface is over-generalized, yet the compiler performs the necessary checks
                to
                			   ensure that role, base and team instances are indeed compatible and additionally the return type of <code>migrateToTeam</code>
                			   is checked as a self-type, i.e., it reflects the exact type of the call target.
             </p>
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          <div class="breadcrumb"><a class="nav" href="s6.html" rel="section">&sect;6&nbsp;Object Teams API</a>&nbsp;&gt;&nbsp;<a class="nav" href="s6.2.html" rel="section">&sect;6.2&nbsp;Other API Elements</a></div>
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                  width="88" /></a><address>&copy; Stephan Herrmann, Christine Hundt, Marco Mosconi</address>
          			OT/J version 1.3 &mdash; last modified: 2011-05-15
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	<td class="back"><a id="top"></a><a href="s6.2.d.html" rel="prev"><< §6.2.(d) Exceptions</a></td>
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	<div class="breadcrumb"><a class="nav" href="s6.html" rel="section">§6 Object Teams API</a> > <a class="nav" href="s6.2.html" rel="section">§6.2 Other API Elements</a></div>
	<div class="subsect depth3" id="s6.2.e">
	<h4 class="subsect">§6.2.(e) <span class="title">Role migration</span><a class="img" href="s6.2.e.html" title="PermaLink to (e) Role migration"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png"
	alt="" /></a></h4>
	<p>The following interfaces can be used to enable role migration:</p>
	<dl>
	<dt><code>IBaseMigratable</code></dt>
	<dd>This interface declares a method
	<div class="listing plain"><pre>
	<code><B> <b>void</b> migrateToBase(B otherBase)</code> </pre></div>
	and instructs the compiler to generate an implementation of this method
	for any bound role declaring <code>IBaseMigratable</code> as its super-interface.<br />
	The effect of calling <code>migrateToBase</code> on a role instance is to re-bind this role to a new base instance.
	The base instance must be compatible to the role's base class (in order to avoid problems during lifting the
	compiler may require the base to be of the exact type of the role's base class).
	Passing <code>null</code> to this method causes an <code>NullPointerException</code> to be thrown.
	</dd>
	<dt><code>ITeamMigratable</code></dt>
	<dd>This interface declares a method
	<div class="listing plain"><pre>
	<code><R> R<@otherTeam> migrateToTeam(<b>final</b> ITeam otherTeam)</code></pre></div>
	and instructs the compiler to
	generate an implementation of this method for any role declaring <code>ITeamMigratable</code> as its super-interface.<br />
	The effect of calling <code>migrateToTeam</code> on a role instance is to re-bind this role to become a contained part of a new team instance.
	The team instance must be of the exact type of the role's enclosing team.
	Passing <code>null</code> to this method causes a <code>NullPointerException</code> to be thrown.<br /><div class="note">
	<h5>Caveat:</h5>
	This method intentionally breaks the rules of family polymorphism: any reference <code>R<@previousTeam> r</code>
	which was established before migration will incorrectly imply that the role's enclosing team still is <code>previousTeam</code>,
	which is no longer true after migration.
	While this does not effect any method lookup (which is still safe), further assumptions based on a role's dependent type
	are invalidated by team migration. The same holds for references from the migrating role to any sibling role instances.<br />
	If the rules of family polymorphism should be maintained one should just refrain from declaring <code>ITeamMigratable</code>
	as a role's super-interface.
	</div>
	</dd>
	</dl>
	<p>For both methods the signature declared in the interface is over-generalized, yet the compiler performs the necessary checks
	to
	ensure that role, base and team instances are indeed compatible and additionally the return type of <code>migrateToTeam</code>
	is checked as a self-type, i.e., it reflects the exact type of the call target.
	</p>
	</div>
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	<div class="breadcrumb"><a class="nav" href="s6.html" rel="section">§6 Object Teams API</a> > <a class="nav" href="s6.2.html" rel="section">§6.2 Other API Elements</a></div>
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	OT/J version 1.3 — last modified: 2011-05-15
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