plugins/org.eclipse.objectteams.otdt.ui.help/guide/otjld/xdef/s5.4.1.html - objectteams/org.eclipse.objectteams - Gitiles

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                <td class="back"><a id="top"></a><a href="s5.4.c.html" rel="prev">&lt;&lt;&nbsp;&sect;5.4.(c)&nbsp;Exceptions</a></td>
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          <div class="breadcrumb"><a class="nav" href="s5.html" rel="section">&sect;5&nbsp;Team Activation</a>&nbsp;&gt;&nbsp;<a class="nav" href="s5.4.html" rel="section">&sect;5.4&nbsp;Guard predicates</a></div>
          <div class="sect depth3" id="s5.4.1">
             <h3 class="sect">&sect;5.4.1&nbsp;Regular guards<a class="img" href="s5.4.1.html"
                   title="PermaLink to &sect;5.4.1&nbsp;Regular guards"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png"
                        alt="" /></a></h3>
             <p>This group of guards evaluates within the context of a given role.
                		These guards are evaluated <em>after</em> a callin target is lifted and
                		<em>before</em> a callin bound role method is invoked.

             </p>
             <div class="subsect depth4" id="s5.4.1.a">
                <h4 class="subsect">(a)&nbsp;<span class="title">Method binding guards</span><a class="img" href="s5.4.1.a.html"
                      title="PermaLink to (a)&nbsp;Method binding guards"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png"
                           alt="" /></a></h4>
                <p>A guard may be attached to a callin method binding as in:

                </p>
                <div class="listing plain"><pre><b>void</b> roleMethod(<b>int</b> ir) <b>&lt;-</b> <b>after</b> <b>void</b> baseMethod(<b>int</b> ib)
   <b>when</b> (ir &gt; MyTeam.this.threshold);</pre></div>
                <p>Such a guard only affects the callin binding to which it is attached,
                   			i.e., this specific callin binding is only effective,
                   			if the predicate evaluates to <code>true</code>.
                   			<br />
                   			The following values are within the scope of the predicate expression,
                   			and thus can be used to express the condition:

                </p>
                <ul>
                   <li>The role instance denoted by <code>this</code>.<br />
                      				Features of the role instance can also be accessed relative to
                      				<code>this</code> with or without explicit qualifying <code>this</code>.

                   </li>
                   <li>The team instance denoted by a qualified this reference as in
                      				<code>MyTeam.this</code>.

                   </li>
                   <li>If the callin binding includes signatures (as in the example above):
                      				Parameters of the role method.<br />
                      				If parameter mappings are involved, they will be evaluated before evaluating the guard.

                   </li>
                </ul>
             </div>
             <div class="subsect depth4" id="s5.4.1.b">
                <h4 class="subsect">(b)&nbsp;<span class="title">Method guards</span><a class="img" href="s5.4.1.b.html" title="PermaLink to (b)&nbsp;Method guards"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png"
                           alt="" /></a></h4>
                <p>A method guard is similar to a method binding guard, but it applies
                   			to all callin method bindings of this method.<br />
                   			A method guard is declared between the method signature and the method body:

                </p>
                <div class="listing plain"><pre><b>void</b> roleMethod(<b>int</b> ir)
   <b>when</b> (ir &gt; MyTeam.this.threshold) { <i>body statements</i> }</pre></div>
             </div>
             <div class="subsect depth4" id="s5.4.1.c">
                <h4 class="subsect">(c)&nbsp;<span class="title">Role level guards</span><a class="img" href="s5.4.1.c.html"
                      title="PermaLink to (c)&nbsp;Role level guards"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png"
                           alt="" /></a></h4>
                <p>When a guard is specified at the role level, i.e., directly before the
                   			class body of a role class, it applies to all callin method bindings of
                   			the role class:

                </p>
                <div class="listing plain"><pre><b>protected</b> <b>class</b> MyRole
   <b>when</b> (value &gt; MyTeam.this.threshold)
 {
     <b>int</b> value;
     <i>other <b>class</b> body declarations</i>
 }</pre></div>
                <p>The following values are within the scope of the predicate expression:

                </p>
                <ul>
                   <li>The role instance denoted by <code>this</code> (explicit or implicit, see above).
                      				Thus, in the example <code>value</code> will be interpreted as a field of the enclosing role.

                   </li>
                   <li>The team instance denoted by a qualified this reference as in <code>MyTeam.this</code></li>
                </ul>
             </div>
             <div class="subsect depth4" id="s5.4.1.d">
                <h4 class="subsect">(d)&nbsp;<span class="title">Team level guards</span><a class="img" href="s5.4.1.d.html"
                      title="PermaLink to (d)&nbsp;Team level guards"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png"
                           alt="" /></a></h4>
                <p>A guard specified in the header of a team class may disable the callin
                   			bindings of all contained role classes. The syntax corresponds to the syntax
                   			of role level guards.<br />
                   			The only value directly available within team level guard is the
                   			team instance (denoted by <code>this</code>) and its features.

                </p>
             </div>
             <p>Of course all guards can also access any visible static feature of a visible class.

             </p>
             <p>Even if a guard has no direct effect, because, e.g., a role class has no callin
                		bindings (maybe not even a role-base binding), predicates at such abstract
                		levels are useful, because all predicates are inherited by all sub classes
                		(explicit and implicit).

             </p>
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                <td class="next"><a href="s5.4.2.html" rel="next">&sect;5.4.2&nbsp;Base guards&nbsp;&gt;&gt;</a></td>
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          <div class="breadcrumb"><a class="nav" href="s5.html" rel="section">&sect;5&nbsp;Team Activation</a>&nbsp;&gt;&nbsp;<a class="nav" href="s5.4.html" rel="section">&sect;5.4&nbsp;Guard predicates</a></div>
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          			OT/J version 1.3 &mdash; last modified: 2010-10-05
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	<td class="back"><a id="top"></a><a href="s5.4.c.html" rel="prev"><< §5.4.(c) Exceptions</a></td>
	<td class="top"><a href="index.html" rel="contents">↑ Table of Contents ↑</a></td>
	<td class="next"><a href="s5.4.2.html" rel="next">§5.4.2 Base guards >></a></td>
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	<div class="breadcrumb"><a class="nav" href="s5.html" rel="section">§5 Team Activation</a> > <a class="nav" href="s5.4.html" rel="section">§5.4 Guard predicates</a></div>
	<div class="sect depth3" id="s5.4.1">
	<h3 class="sect">§5.4.1 Regular guards<a class="img" href="s5.4.1.html"
	title="PermaLink to §5.4.1 Regular guards"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png"
	alt="" /></a></h3>
	<p>This group of guards evaluates within the context of a given role.
	These guards are evaluated <em>after</em> a callin target is lifted and
	<em>before</em> a callin bound role method is invoked.

	</p>
	<div class="subsect depth4" id="s5.4.1.a">
	<h4 class="subsect">(a) <span class="title">Method binding guards</span><a class="img" href="s5.4.1.a.html"
	title="PermaLink to (a) Method binding guards"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png"
	alt="" /></a></h4>
	<p>A guard may be attached to a callin method binding as in:

	</p>
	<div class="listing plain"><pre><b>void</b> roleMethod(<b>int</b> ir) <b><-</b> <b>after</b> <b>void</b> baseMethod(<b>int</b> ib)
	<b>when</b> (ir > MyTeam.this.threshold);</pre></div>
	<p>Such a guard only affects the callin binding to which it is attached,
	i.e., this specific callin binding is only effective,
	if the predicate evaluates to <code>true</code>.
	<br />
	The following values are within the scope of the predicate expression,
	and thus can be used to express the condition:

	</p>
	<ul>
	<li>The role instance denoted by <code>this</code>.<br />
	Features of the role instance can also be accessed relative to
	<code>this</code> with or without explicit qualifying <code>this</code>.

	</li>
	<li>The team instance denoted by a qualified this reference as in
	<code>MyTeam.this</code>.

	</li>
	<li>If the callin binding includes signatures (as in the example above):
	Parameters of the role method.<br />
	If parameter mappings are involved, they will be evaluated before evaluating the guard.

	</li>
	</ul>
	</div>
	<div class="subsect depth4" id="s5.4.1.b">
	<h4 class="subsect">(b) <span class="title">Method guards</span><a class="img" href="s5.4.1.b.html" title="PermaLink to (b) Method guards"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png"
	alt="" /></a></h4>
	<p>A method guard is similar to a method binding guard, but it applies
	to all callin method bindings of this method.<br />
	A method guard is declared between the method signature and the method body:

	</p>
	<div class="listing plain"><pre><b>void</b> roleMethod(<b>int</b> ir)
	<b>when</b> (ir > MyTeam.this.threshold) { <i>body statements</i> }</pre></div>
	</div>
	<div class="subsect depth4" id="s5.4.1.c">
	<h4 class="subsect">(c) <span class="title">Role level guards</span><a class="img" href="s5.4.1.c.html"
	title="PermaLink to (c) Role level guards"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png"
	alt="" /></a></h4>
	<p>When a guard is specified at the role level, i.e., directly before the
	class body of a role class, it applies to all callin method bindings of
	the role class:

	</p>
	<div class="listing plain"><pre><b>protected</b> <b>class</b> MyRole
	<b>when</b> (value > MyTeam.this.threshold)
	{
	<b>int</b> value;
	<i>other <b>class</b> body declarations</i>
	}</pre></div>
	<p>The following values are within the scope of the predicate expression:

	</p>
	<ul>
	<li>The role instance denoted by <code>this</code> (explicit or implicit, see above).
	Thus, in the example <code>value</code> will be interpreted as a field of the enclosing role.

	</li>
	<li>The team instance denoted by a qualified this reference as in <code>MyTeam.this</code></li>
	</ul>
	</div>
	<div class="subsect depth4" id="s5.4.1.d">
	<h4 class="subsect">(d) <span class="title">Team level guards</span><a class="img" href="s5.4.1.d.html"
	title="PermaLink to (d) Team level guards"><img style="vertical-align:text-top;margin-left:5px;" src="../images/permalink.png"
	alt="" /></a></h4>
	<p>A guard specified in the header of a team class may disable the callin
	bindings of all contained role classes. The syntax corresponds to the syntax
	of role level guards.<br />
	The only value directly available within team level guard is the
	team instance (denoted by <code>this</code>) and its features.

	</p>
	</div>
	<p>Of course all guards can also access any visible static feature of a visible class.

	</p>
	<p>Even if a guard has no direct effect, because, e.g., a role class has no callin
	bindings (maybe not even a role-base binding), predicates at such abstract
	levels are useful, because all predicates are inherited by all sub classes
	(explicit and implicit).

	</p>
	</div>
	<table class="nav">
	<tr>
	<td class="back"><a href="s5.4.c.html" rel="prev"><< §5.4.(c) Exceptions</a></td>
	<td class="top"><a href="index.html" rel="contents">↑ Table of Contents ↑</a></td>
	<td class="next"><a href="s5.4.2.html" rel="next">§5.4.2 Base guards >></a></td>
	</tr>
	</table>
	<div class="breadcrumb"><a class="nav" href="s5.html" rel="section">§5 Team Activation</a> > <a class="nav" href="s5.4.html" rel="section">§5.4 Guard predicates</a></div>
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	width="88" /></a><address>© Stephan Herrmann, Christine Hundt, Marco Mosconi</address>
	OT/J version 1.3 — last modified: 2010-10-05
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