Register.h

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00001 //# Register.h: Templated function to provide simple type identification
00002 //# Copyright (C) 1993,1994,1995,1999,2001
00003 //# Associated Universities, Inc. Washington DC, USA.
00004 //#
00005 //# This library is free software; you can redistribute it and/or modify it
00006 //# under the terms of the GNU Library General Public License as published by
00007 //# the Free Software Foundation; either version 2 of the License, or (at your
00008 //# option) any later version.
00009 //#
00010 //# This library is distributed in the hope that it will be useful, but WITHOUT
00011 //# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
00012 //# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
00013 //# License for more details.
00014 //#
00015 //# You should have received a copy of the GNU Library General Public License
00016 //# along with this library; if not, write to the Free Software Foundation,
00017 //# Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
00018 //#
00019 //# Correspondence concerning AIPS++ should be addressed as follows:
00020 //#        Internet email: aips2-request@nrao.edu.
00021 //#        Postal address: AIPS++ Project Office
00022 //#                        National Radio Astronomy Observatory
00023 //#                        520 Edgemont Road
00024 //#                        Charlottesville, VA 22903-2475 USA
00025 //#
00026 //# $Id$
00027 
00028 #ifndef CASA_REGISTER_H
00029 #define CASA_REGISTER_H
00030 
00031 #include <casacore/casa/aips.h>
00032 #include <casacore/casa/Utilities/RegSequence.h>
00033 
00034 namespace casacore { //# NAMESPACE CASACORE - BEGIN
00035 
00036 // <summary> 
00037 //    Primitive Run Time Type Information (<em>RTTI</em>)
00038 // </summary>
00039 //
00040 // <use visibility=export>
00041 // <reviewed reviewer="UNKNOWN" date="before2004/08/25" tests="" demos=""></reviewed>
00042 //
00043 // <prerequisite>
00044 //   <li> <em>none</em>
00045 // </prerequisite>
00046 //
00047 // <etymology>
00048 //    This function is called Register because the user is <em>registering</em>
00049 //    a type with the run-time type mechanism.
00050 // </etymology>
00051 //
00052 // <synopsis> 
00053 //    This function returns a unique unsigned integer (<b>uInt</b>) for each
00054 //    type of pointer the user passes in as a parameter. It will always return
00055 //    the same number for a given type during a particular execution. The
00056 //    unsigned integer which is returned can be use to identify the particular
00057 //    type.
00058 //
00059 //    <note role=warning> This function does not work correctly for
00060 //          <em>multiple inheritance</em>, but <b>ONLY</b> for 
00061 //          <em>single inheritance</em>. In addition, the type <em>number</em>
00062 //          which is returned is <b>NOT</b> unique across program executions.
00063 //    </note>
00064 //
00065 //    This RTTI mechanism is simple, it does not require extra functions to be
00066 //    added to the classes which are to be <em>identified</em>, and it is 
00067 //    similar to the RTTI mechanism which will be a part of the C++ language
00068 //    in the future.
00069 //
00070 //    To be useful, however, this mechanism must be used as part of the
00071 //    implementation of a <em>virtual</em> member function. For example:
00072 //    <srcblock>
00073 //    #include <casacore/casa/Utilities/Register.h>
00074 // #include <iostream>
00075 //    
00076 //    class foo { public: virtual uInt type() { return Register(this);}};
00077 //    class bar : public foo { public: uInt type() { return Register(this);}};
00078 //    main() {
00079 //        foo *b = new bar();
00080 //        foo *f = new foo();
00081 //    
00082 //        cout << "f: type()=" << f->type() << " Register()=" << Register(f) << endl;
00083 //        cout << "b: type()=" << b->type() << " Register()=" << Register(b) << endl;
00084 //    }
00085 //    </srcblock>
00086 //    The output of this code would look something like:
00087 //    <pre>
00088 //        f: type()=1 Register()=1
00089 //        b: type()=2 Register()=1
00090 //    </pre>
00091 //    Without the virtual function, <src>type()</src>, the output of 
00092 //    <src>Register()</src> is deceiving and of little use.
00093 // </synopsis> 
00094 //
00095 // <motivation>
00096 //      Needed a simple type identification mechanism for the
00097 //      <linkto class=Notice>Notice</linkto> class. This was necessary so that
00098 //      multiple notices could be distinguished.
00099 //      It can be replaced by the future standard RTTI.
00100 // </motivation>
00101 //
00102 // <templating arg=t>
00103 //    <li> <em>none</em>
00104 // </templating>
00105 //
00106 // <group name=register>
00107 
00108 // This is a templated function which takes a pointer to any class as a parameter.
00109 // The parameter's type is then used to generate a unique id. The parameter is
00110 // a pointer rather than a <em>value</em> for efficiency reasons. With a 
00111 // <em>value</em> parameter, it would be difficult to do things like:
00112 // <srcblock>
00113 //    Register(static_cast<MyClass*>(0));
00114 // </srcblock>
00115 // to find the <src>Register</src> type id for a random class.
00116 template<class t> uInt Register(const t *);
00117 
00118 // </group>
00119 
00120 // Bother!!
00121 // template<class t> inline uInt Register(const t *) {
00122 //   static uInt type = 0;
00123 //   if (!type) type = RegSequence::SgetNext();
00124 //   return type;
00125 // }
00126 
00127 // BOTHER!! BOTHER!! BOTHER!!
00128 // template<class t> inline uInt Register(const t &v) {
00129 //   return Register(&v);
00130 // }
00131 
00132 
00133 } //# NAMESPACE CASACORE - END
00134 
00135 #ifndef CASACORE_NO_AUTO_TEMPLATES
00136 #include <casacore/casa/Utilities/Register.tcc>
00137 #endif //# CASACORE_NO_AUTO_TEMPLATES
00138 #endif
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