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<h1>2 OMG IDL</h1>
<h3><a name="id61149">2.1
OMG IDL - Overview</a></h3>
<p>The purpose of OMG IDL, <strong>Interface Definition Language</strong>, mapping
is to act as translator between platforms and languages. An IDL
specification is supposed to describe data types, object types etc.</p>
<p>Since the <span class="code">C</span> and <span class="code">Java</span> IC backends only supports a subset of the
IDL types supported by the other backends, the mapping is divided into
different parts. For more information about IDL to Erlang mapping,
i.e., <span class="code">CORBA</span>, plain Erlang and generic Erlang Server, see the Orber
User's Guide. How to use the plain Erlang and generic Erlang Server is
found in this User's Guide.</p>
<h4>Reserved Compiler Names and Keywords</h4>
<p>The use of some names is strongly discouraged due to
ambiguities. However, the use of some names is prohibited
when using the Erlang mapping , as they are strictly reserved for IC.</p>
<p>IC reserves all identifiers starting with <span class="code">OE_</span> and <span class="code">oe_</span>
for internal use.</p>
<p>Note also, that an identifier in IDL can contain alphabetic,
digits and underscore characters, but the first character
<strong>must</strong> be alphabetic.
</p>
<p>Using underscores in IDL names can lead to ambiguities
due to the name mapping described above. It is advisable to
avoid the use of underscores in identifiers.</p>
<p>The OMG defines a set of reserved words, shown below, for use as keywords.
These may <strong>not</strong> be used as, for example, identifiers.</p>
<table border="1" cellpadding="2" cellspacing="0">
<tr>
<td align="left" valign="middle">abstract</td>
<td align="left" valign="middle">double</td>
<td align="left" valign="middle">local</td>
<td align="left" valign="middle">raises</td>
<td align="left" valign="middle">typedef</td>
</tr>
<tr>
<td align="left" valign="middle">any</td>
<td align="left" valign="middle">exception</td>
<td align="left" valign="middle">long</td>
<td align="left" valign="middle">readonly</td>
<td align="left" valign="middle">unsigned</td>
</tr>
<tr>
<td align="left" valign="middle">attribute</td>
<td align="left" valign="middle">enum</td>
<td align="left" valign="middle">module</td>
<td align="left" valign="middle">sequence</td>
<td align="left" valign="middle">union</td>
</tr>
<tr>
<td align="left" valign="middle">boolean</td>
<td align="left" valign="middle">factory</td>
<td align="left" valign="middle">native</td>
<td align="left" valign="middle">short</td>
<td align="left" valign="middle">ValueBase</td>
</tr>
<tr>
<td align="left" valign="middle">case</td>
<td align="left" valign="middle">FALSE</td>
<td align="left" valign="middle">Object</td>
<td align="left" valign="middle">string</td>
<td align="left" valign="middle">valuetype</td>
</tr>
<tr>
<td align="left" valign="middle">char</td>
<td align="left" valign="middle">fixed</td>
<td align="left" valign="middle">octet</td>
<td align="left" valign="middle">struct</td>
<td align="left" valign="middle">void</td>
</tr>
<tr>
<td align="left" valign="middle">const</td>
<td align="left" valign="middle">float</td>
<td align="left" valign="middle">oneway</td>
<td align="left" valign="middle">supports</td>
<td align="left" valign="middle">wchar</td>
</tr>
<tr>
<td align="left" valign="middle">context</td>
<td align="left" valign="middle">in</td>
<td align="left" valign="middle">out</td>
<td align="left" valign="middle">switch</td>
<td align="left" valign="middle">wstring</td>
</tr>
<tr>
<td align="left" valign="middle">custom</td>
<td align="left" valign="middle">inout</td>
<td align="left" valign="middle">private</td>
<td align="left" valign="middle">TRUE</td>
<td align="left" valign="middle"></td>
</tr>
<tr>
<td align="left" valign="middle">default</td>
<td align="left" valign="middle">interface</td>
<td align="left" valign="middle">public</td>
<td align="left" valign="middle">truncatable</td>
<td align="left" valign="middle"></td>
</tr>
</table>
<em>Table
2.1:
OMG IDL keywords</em>
<p>The keywords listed above must be written exactly as shown. Any usage
of identifiers that collide with a keyword is illegal. For example,
<strong>long</strong> is a valid keyword; <strong>Long</strong> and <strong>LONG</strong> are
illegal as keywords and identifiers. But, since the OMG must be able
to expand the IDL grammar, it is possible to use <strong>Escaped Identifiers</strong>. For example, it is not unlikely that <span class="code">native</span>
have been used in IDL-specifications as identifiers. One option is to
change all occurrences to <span class="code">myNative</span>. Usually, it is necessary
to change programming language code that depends upon that IDL as well.
Since Escaped Identifiers just disable type checking (i.e. if it is a reserved
word or not) and leaves everything else unchanged, it is only necessary to
update the IDL-specification. To escape an identifier, simply prefix it
with <span class="code">_</span>. The following IDL-code is illegal:</p>
<div class="example"><pre>
typedef string native;
interface i {
void foo(in native Arg);
};
};
</pre></div>
<p>With Escaped Identifiers the code will look like:</p>
<div class="example"><pre>
typedef string _native;
interface i {
void foo(in _native Arg);
};
};
</pre></div>
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