<?xml version="1.0" encoding="latin1" ?>
<!DOCTYPE chapter SYSTEM "chapter.dtd">
<chapter>
<header>
<copyright>
<year>2002</year><year>2009</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
</copyright>
<legalnotice>
The contents of this file are subject to the Erlang Public License,
Version 1.1, (the "License"); you may not use this file except in
compliance with the License. You should have received a copy of the
Erlang Public License along with this software. If not, it can be
retrieved online at http://www.erlang.org/.
Software distributed under the License is distributed on an "AS IS"
basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
the License for the specific language governing rights and limitations
under the License.
</legalnotice>
<title>OMG IDL</title>
<prepared></prepared>
<docno></docno>
<date>2002-07-15</date>
<rev></rev>
<file>ch_basic_idl.xml</file>
</header>
<section>
<title>OMG IDL - Overview</title>
<p>The purpose of OMG IDL, <em>Interface Definition Language</em>, 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 <c>C</c> and <c>Java</c> 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., <c>CORBA</c>, 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>
<section>
<title>Reserved Compiler Names and Keywords</title>
<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 <c>OE_</c> and <c>oe_</c>
for internal use.</p>
<p>Note also, that an identifier in IDL can contain alphabetic,
digits and underscore characters, but the first character
<em>must</em> 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 <em>not</em> be used as, for example, identifiers.</p>
<table>
<row>
<cell align="left" valign="middle">abstract</cell>
<cell align="left" valign="middle">double</cell>
<cell align="left" valign="middle">local</cell>
<cell align="left" valign="middle">raises</cell>
<cell align="left" valign="middle">typedef</cell>
</row>
<row>
<cell align="left" valign="middle">any</cell>
<cell align="left" valign="middle">exception</cell>
<cell align="left" valign="middle">long</cell>
<cell align="left" valign="middle">readonly</cell>
<cell align="left" valign="middle">unsigned</cell>
</row>
<row>
<cell align="left" valign="middle">attribute</cell>
<cell align="left" valign="middle">enum</cell>
<cell align="left" valign="middle">module</cell>
<cell align="left" valign="middle">sequence</cell>
<cell align="left" valign="middle">union</cell>
</row>
<row>
<cell align="left" valign="middle">boolean</cell>
<cell align="left" valign="middle">factory</cell>
<cell align="left" valign="middle">native</cell>
<cell align="left" valign="middle">short</cell>
<cell align="left" valign="middle">ValueBase</cell>
</row>
<row>
<cell align="left" valign="middle">case</cell>
<cell align="left" valign="middle">FALSE</cell>
<cell align="left" valign="middle">Object</cell>
<cell align="left" valign="middle">string</cell>
<cell align="left" valign="middle">valuetype</cell>
</row>
<row>
<cell align="left" valign="middle">char</cell>
<cell align="left" valign="middle">fixed</cell>
<cell align="left" valign="middle">octet</cell>
<cell align="left" valign="middle">struct</cell>
<cell align="left" valign="middle">void</cell>
</row>
<row>
<cell align="left" valign="middle">const</cell>
<cell align="left" valign="middle">float</cell>
<cell align="left" valign="middle">oneway</cell>
<cell align="left" valign="middle">supports</cell>
<cell align="left" valign="middle">wchar</cell>
</row>
<row>
<cell align="left" valign="middle">context</cell>
<cell align="left" valign="middle">in</cell>
<cell align="left" valign="middle">out</cell>
<cell align="left" valign="middle">switch</cell>
<cell align="left" valign="middle">wstring</cell>
</row>
<row>
<cell align="left" valign="middle">custom</cell>
<cell align="left" valign="middle">inout</cell>
<cell align="left" valign="middle">private</cell>
<cell align="left" valign="middle">TRUE</cell>
<cell align="left" valign="middle"></cell>
</row>
<row>
<cell align="left" valign="middle">default</cell>
<cell align="left" valign="middle">interface</cell>
<cell align="left" valign="middle">public</cell>
<cell align="left" valign="middle">truncatable</cell>
<cell align="left" valign="middle"></cell>
</row>
<tcaption>OMG IDL keywords</tcaption>
</table>
<p>The keywords listed above must be written exactly as shown. Any usage
of identifiers that collide with a keyword is illegal. For example,
<em>long</em> is a valid keyword; <em>Long</em> and <em>LONG</em> are
illegal as keywords and identifiers. But, since the OMG must be able
to expand the IDL grammar, it is possible to use <em>Escaped Identifiers</em>. For example, it is not unlikely that <c>native</c>
have been used in IDL-specifications as identifiers. One option is to
change all occurrences to <c>myNative</c>. 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 <c>_</c>. The following IDL-code is illegal:</p>
<code type="none">
typedef string native;
interface i {
void foo(in native Arg);
};
};
</code>
<p>With Escaped Identifiers the code will look like:</p>
<code type="none">
typedef string _native;
interface i {
void foo(in _native Arg);
};
};
</code>
</section>
</section>
</chapter>
