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| <td class="back"><a id="top"></a><a href="s4.4.a.html" rel="prev"><< §4.4.(a) General case parameter mapping</a></td> |
| <td class="top"><a href="index.html" rel="contents">↑ Table of Contents ↑</a></td> |
| <td class="next"><a href="s4.4.c.html" rel="next">§4.4.(c) Mapping the result of a base method >></a></td> |
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| <div class="breadcrumb"><a class="nav" href="s4.html" rel="section">§4 Callin Binding</a> > <a class="nav" href="s4.4.html" rel="section">§4.4 Callin parameter mapping</a></div> |
| <div class="subsect depth3" id="s4.4.b"> |
| <h4 class="subsect">§4.4.(b) <span class="title">Restrictions for callin replace bindings</span><a class="img" href="s4.4.b.html" |
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| <p>The right-hand side of a parameter mapping may either be |
| the simple name of a base method argument without further computation, |
| or an arbitrary expression <em>not</em> containing any base method argument. |
| <br /> |
| Each base method argument must either appear as a simple name in exactly one parameter mapping |
| or not be mapped at all. In the latter case, the original argument is "tunneled" to |
| the base call, meaning, the callin method does not see the argument, but it is passed |
| to the base method as expected. |
| <br /> |
| If the base method declares a result, then |
| |
| </p> |
| <ul> |
| <li>if the role method also declares a result, <code>result</code> must be mapped to itself: |
| <br /><code>result -> result</code></li> |
| <li>if the role method does not declare a result, an arbitrary expression may be mapped to result: |
| <br /><code><em>expression</em> -> result</code><br /> |
| If in this situation no result mapping exists, the result of the base call |
| is "tunneled" and passed to the original caller (see <a href="s4.3.e.html" title="§4.3.(e) Fragile callin binding" |
| class="sect"> |
| fragile callin binding (§4.3.(e))</a> above). |
| |
| </li> |
| </ul> |
| <p>These rules ensure that these bindings are reversible |
| for the sake of base calls (<a href="s4.3.html" title="§4.3 Base calls" class="sect">§4.3</a>). |
| |
| </p> |
| <p>As stated above a fragile callin binding (<a href="s4.3.e.html" title="§4.3.(e) Fragile callin binding" |
| class="sect">§4.3.(e)</a>) |
| is not allowed with a callin method that definitely has no base call |
| (<a href="s4.3.b.html" title="§4.3.(b) Missing base call" |
| class="sect">§4.3.(b)</a>). A callin replace binding is not fragile if it provides |
| the base result using a result mapping. |
| |
| </p> |
| <p>A callin method bound with replace to a base method returning |
| void must not declare a non-void result. |
| |
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| <td class="next"><a href="s4.4.c.html" rel="next">§4.4.(c) Mapping the result of a base method >></a></td> |
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| <div class="breadcrumb"><a class="nav" href="s4.html" rel="section">§4 Callin Binding</a> > <a class="nav" href="s4.4.html" rel="section">§4.4 Callin parameter mapping</a></div> |
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