base/TypeManip

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/****************************************************************************
  Copyright (C)2001 by Andrei Alexandrescu

  This file is a derivative of a file from the Loki Library written by
  Andrei Alexandrescu.  It was distributed by him under the terms
  listed below (titled Loki Original Distribution Terms).
  In accordance with the terms, this distribution contains the copyright
  notice here and the copyright notice and permission notice
  in supporting documentation.  The terms do *not* require
  redistribution under those same terms.  This code is distributed
  to you under the terms of the GNU General Public License (GPL) 
  below.  The GPL does not require you to maintain the terms of
  the Loki Original Distribution Terms, but you are encouraged to do so.

  This program/file is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation; either version 2 of the License, or
  (at your option) any later version.
  
  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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  You should have received a copy of the GNU General Public License
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 ****************************************************************************
  Loki Original Distribution Terms:

  The Loki Library
  Copyright (c) 2001 by Andrei Alexandrescu
  This code accompanies the book:
  Alexandrescu, Andrei. "Modern C++ Design: Generic Programming and Design 
      Patterns Applied". Copyright (c) 2001. Addison-Wesley.
  Permission to use, copy, modify, distribute and sell this software for any 
      purpose is hereby granted without fee, provided that the above copyright 
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      permission notice appear in supporting documentation.
  The author or Addison-Welsey Longman make no representations about the 
      suitability of this software for any purpose. It is provided "as is" 
      without express or implied warranty.
 ****************************************************************************

  $Id: TypeManip 1029 2004-02-11 20:45:54Z jungd $
  $Revision: 1.1 $
  $Date: 2004-02-11 15:45:54 -0500 (Wed, 11 Feb 2004) $
  $Author: jungd $
 
****************************************************************************/

// Last update: June 20, 2001

#ifndef TYPEMANIP_INC_
#define TYPEMANIP_INC_

namespace base
{
////////////////////////////////////////////////////////////////////////////////
// class template Int2Type
// Converts each integral constant into a unique type
// Invocation: Int2Type<v> where v is a compile-time constant integral
// Defines 'value', an enum that evaluates to v
////////////////////////////////////////////////////////////////////////////////

    template <int v>
    struct Int2Type
    {
        enum { value = v };
    };
    
////////////////////////////////////////////////////////////////////////////////
// class template Type2Type
// Converts each type into a unique, insipid type
// Invocation Type2Type<T> where T is a type
// Defines the type OriginalType which maps back to T
////////////////////////////////////////////////////////////////////////////////

    template <typename T>
    struct Type2Type
    {
        typedef T OriginalType;
    };
    
////////////////////////////////////////////////////////////////////////////////
// class template Select
// Selects one of two types based upon a boolean constant
// Invocation: Select<flag, T, U>::Result
// where:
// flag is a compile-time boolean constant
// T and U are types
// Result evaluates to T if flag is true, and to U otherwise.
////////////////////////////////////////////////////////////////////////////////

    template <bool flag, typename T, typename U>
    struct Select
    {
        typedef T Result;
    };
    template <typename T, typename U>
    struct Select<false, T, U>
    {
        typedef U Result;
    };
    
////////////////////////////////////////////////////////////////////////////////
// Helper types Small and Big - guarantee that sizeof(Small) < sizeof(Big)
////////////////////////////////////////////////////////////////////////////////

    namespace Private
    {
        template <class T, class U>
        struct ConversionHelper
        {
            typedef char Small;
            struct Big { char dummy[2]; };
            static Big   Test(...);
            static Small Test(U);
            static T MakeT();
        };
    }

////////////////////////////////////////////////////////////////////////////////
// class template Conversion
// Figures out the conversion relationships between two types
// Invocations (T and U are types):
// a) Conversion<T, U>::exists
// returns (at compile time) true if there is an implicit conversion from T
// to U (example: Derived to Base)
// b) Conversion<T, U>::exists2Way
// returns (at compile time) true if there are both conversions from T
// to U and from U to T (example: int to char and back)
// c) Conversion<T, U>::sameType
// returns (at compile time) true if T and U represent the same type
//
// Caveat: might not work if T and U are in a private inheritance hierarchy.
////////////////////////////////////////////////////////////////////////////////

    template <class T, class U>
    struct Conversion
    {
        typedef Private::ConversionHelper<T, U> H;
#ifndef __MWERKS__
        enum { exists = sizeof(typename H::Small) == sizeof(H::Test(H::MakeT())) };
#else
        enum { exists = false };
#endif
        enum { exists2Way = exists && Conversion<U, T>::exists };
        enum { sameType = false };
    };
    
    template <class T>
    struct Conversion<T, T>    
    {
        enum { exists = 1, exists2Way = 1,sameType = 1 };
    };
    
    template <class T>
    struct Conversion<void, T>    
    {
        enum { exists = 1, exists2Way = 0,sameType = 0 };
    };
    
    template <class T>
    struct Conversion<T, void>    
    {
        enum { exists = 1, exists2Way = 0,sameType = 0 };
    };
    
    template <>
    class Conversion<void, void>    
    {
    public:
        enum { exists = 1, exists2Way = 1,sameType = 1 };
    };    
}

////////////////////////////////////////////////////////////////////////////////
// macro SUPERSUBCLASS
// Invocation: SUPERSUBCLASS(B, D) where B and D are types. 
// Returns true if B is a public base of D, or if B and D are aliases of the 
// same type.
//
// Caveat: might not work if T and U are in a private inheritance hierarchy.
////////////////////////////////////////////////////////////////////////////////

#define SUPERSUBCLASS(T, U) \
    (::base::Conversion<const U*, const T*>::exists && \
    !::base::Conversion<const T*, const void*>::sameType)

////////////////////////////////////////////////////////////////////////////////
// macro SUPERSUBCLASS
// Invocation: SUPERSUBCLASS(B, D) where B and D are types. 
// Returns true if B is a public base of D.
//
// Caveat: might not work if T and U are in a private inheritance hierarchy.
////////////////////////////////////////////////////////////////////////////////

#define SUPERSUBCLASS_STRICT(T, U) \
    (SUPERSUBCLASS(T, U) && \
    !::base::Conversion<const T, const U>::sameType)

////////////////////////////////////////////////////////////////////////////////
// Change log:
// June 20, 2001: ported by Nick Thurn to gcc 2.95.3. Kudos, Nick!!!
////////////////////////////////////////////////////////////////////////////////

#endif // TYPEMANIP_INC_

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