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<H1><A NAME="SECTION03170000000000000000">
Implicitly defined methods</A>
</H1>
<P>
The C binding for interfaces and classes includes two methods for
perform type casts. The methods are named <TT>_cast</TT> and
<TT>_cast2</TT>. The leading underscore prevents these built in methods
from conflicting with a user method because user methods cannot begin
with an underscore. Neither of these methods increases the reference
count of the underlying object -- this is contrary to standard
methods that always return new reference counts. Every object has
these two methods, we will use <TT>sidl.BaseClass</TT> as an example. Here are the
signatures for <TT>_cast</TT> and <TT>_cast2</TT> from
<TT>sidl.BaseClass</TT>.
<P>
<BR>
<PRE CLASS="verbatim">sidl_BaseClass
sidl_BaseClass__cast(
void* obj);
void*
sidl_BaseClass__cast2(
void* obj,
const char* type);
</PRE></td></tr></table></blockquote>
<P>
The <TT>_cast</TT> method attempts to cast a SIDL interface or object
pointer to a pointer to <TT>sidl.BaseClass</TT>. The <TT>_cast2</TT>
method attempts to cast a SIDL interface or object pointer to a
pointer to an interface or object pointer of the type named
<TT>type</TT>. In the case of <TT>_cast2</TT>, the client is responsible
for casting the return value into the proper pointer type. Both
methods are <TT>NULL</TT> safe. A <TT>NULL</TT> return value indicates
that the cast failed or that <TT>obj</TT> was <TT>NULL</TT>.
<P>
Non-abstract classes have an additional implicit method called
<TT>_create</TT> to create new instances of the class. Interfaces and
abstract classes do not have this method because you cannot
instantiate them. The <TT>_create</TT> method returns a new reference
that the client must manage. Here is an example of its signature.
<P>
<BR>
<PRE CLASS="verbatim">/**
* Constructor function for the class.
*/
sidl_BaseClass
sidl_BaseClass__create(void);
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<br><br>babel-0.10.2<br>users_guide Last Modified 2005-03-23<br><br><a href="http://www.llnl.gov/CASC/components">http://www.llnl.gov/CASC/components</a><br><a href="mailto:components@llnl.gov">components@llnl.gov</a>
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