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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: Register.h 20551 2009-03-25 00:11:33Z Malte.Marquarding $
00027 
00028 #ifndef CASA_REGISTER_H
00029 #define CASA_REGISTER_H
00030 
00031 #include <casa/Utilities/RegSequence.h>
00032 
00033 namespace casa { //# NAMESPACE CASA - BEGIN
00034 
00035 // <summary> 
00036 //    Primitive Run Time Type Information (<em>RTTI</em>)
00037 // </summary>
00038 //
00039 // <use visibility=export>
00040 // <reviewed reviewer="UNKNOWN" date="before2004/08/25" tests="" demos=""></reviewed>
00041 //
00042 // <prerequisite>
00043 //   <li> <em>none</em>
00044 // </prerequisite>
00045 //
00046 // <etymology>
00047 //    This function is called Register because the user is <em>registering</em>
00048 //    a type with the run-time type mechanism.
00049 // </etymology>
00050 //
00051 // <synopsis> 
00052 //    This function returns a unique unsigned integer (<b>uInt</b>) for each
00053 //    type of pointer the user passes in as a parameter. It will always return
00054 //    the same number for a given type during a particular execution. The
00055 //    unsigned integer which is returned can be use to identify the particular
00056 //    type.
00057 //
00058 //    <note role=warning> This function does not work correctly for
00059 //          <em>multiple inheritance</em>, but <b>ONLY</b> for 
00060 //          <em>single inheritance</em>. In addition, the type <em>number</em>
00061 //          which is returned is <b>NOT</b> unique across program executions.
00062 //    </note>
00063 //
00064 //    This RTTI mechanism is simple, it does not require extra functions to be
00065 //    added to the classes which are to be <em>identified</em>, and it is 
00066 //    similar to the RTTI mechanism which will be a part of the C++ language
00067 //    in the future.
00068 //
00069 //    To be useful, however, this mechanism must be used as part of the
00070 //    implementation of a <em>virtual</em> member function. For example:
00071 //    <srcblock>
00072 //    #include <casa/Utilities/Register.h>
00073 // #include <iostream>
00074 //    
00075 //    class foo { public: virtual uInt type() { return Register(this);}};
00076 //    class bar : public foo { public: uInt type() { return Register(this);}};
00077 //    main() {
00078 //        foo *b = new bar();
00079 //        foo *f = new foo();
00080 //    
00081 //        cout << "f: type()=" << f->type() << " Register()=" << Register(f) << endl;
00082 //        cout << "b: type()=" << b->type() << " Register()=" << Register(b) << endl;
00083 //    }
00084 //    </srcblock>
00085 //    The output of this code would look something like:
00086 //    <pre>
00087 //        f: type()=1 Register()=1
00088 //        b: type()=2 Register()=1
00089 //    </pre>
00090 //    Without the virtual function, <src>type()</src>, the output of 
00091 //    <src>Register()</src> is deceiving and of little use.
00092 // </synopsis> 
00093 //
00094 // <motivation>
00095 //      Needed a simple type identification mechanism for the
00096 //      <linkto class=Notice>Notice</linkto> class. This was necessary so that
00097 //      multiple notices could be distinguished.
00098 //      It can be replaced by the future standard RTTI.
00099 // </motivation>
00100 //
00101 // <templating arg=t>
00102 //    <li> <em>none</em>
00103 // </templating>
00104 //
00105 // <group name=register>
00106 
00107 // This is a templated function which takes a pointer to any class as a parameter.
00108 // The parameter's type is then used to generate a unique id. The parameter is
00109 // a pointer rather than a <em>value</em> for efficiency reasons. With a 
00110 // <em>value</em> parameter, it would be difficult to do things like:
00111 // <srcblock>
00112 //    Register(static_cast<MyClass*>(0));
00113 // </srcblock>
00114 // to find the <src>Register</src> type id for a random class.
00115 template<class t> uInt Register(const t *);
00116 
00117 // </group>
00118 
00119 // Bother!!
00120 // template<class t> inline uInt Register(const t *) {
00121 //   static uInt type = 0;
00122 //   if (!type) type = RegSequence::SgetNext();
00123 //   return type;
00124 // }
00125 
00126 // BOTHER!! BOTHER!! BOTHER!!
00127 // template<class t> inline uInt Register(const t &v) {
00128 //   return Register(&v);
00129 // }
00130 
00131 
00132 } //# NAMESPACE CASA - END
00133 
00134 #ifndef CASACORE_NO_AUTO_TEMPLATES
00135 #include <casa/Utilities/Register.tcc>
00136 #endif //# CASACORE_NO_AUTO_TEMPLATES
00137 #endif