virtual-copy-support.hpp

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/*
  VIRTUAL-COPY-SUPPORT.hpp  -  helper to support copying of erased sub-types
 
   Copyright (C)
     2015,            Hermann Vosseler <Ichthyostega@web.de>
 
 **Lumiera** 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. See the file COPYING for further details.
 
*/
 
 
#ifndef LIB_META_VIRTUAL_COPY_SUPPORT_H
#define LIB_META_VIRTUAL_COPY_SUPPORT_H
 
 
#include "lib/error.hpp"
 
#include <type_traits>
#include <utility>
 
 
namespace lib {
namespace meta{
  
  using std::move;
  
  using std::is_move_constructible;
  using std::is_copy_constructible;
  using std::is_copy_assignable;
  using std::__and_;
  using std::__not_;
  
  namespace error = lumiera::error;
  
  
  
  struct EmptyBase { };
  
  template<class IFA, class BASE = EmptyBase>
  class VirtualCopySupportInterface
    : public BASE
    {
    public:
      virtual ~VirtualCopySupportInterface()  { }
      
      virtual void  copyInto (void* targetStorage)  const =0;
      virtual void  moveInto (void* targetStorage)        =0;
      virtual void  copyInto (IFA&         target)  const =0;
      virtual void  moveInto (IFA&         target)        =0;
    };
  
  
  
  template<class I, class D, class B =I>
  class NoCopyMoveSupport
    : public B
    {
    public:
      virtual void
      copyInto (void*)  const override
        {
          throw error::Logic{"Copy construction invoked but target is noncopyable"};
        }
      
      virtual void
      moveInto (void*)  override
        {
          throw error::Logic{"Move construction invoked but target is noncopyable"};
        }
      
      virtual void
      copyInto (I&)  const override
        {
          throw error::Logic{"Assignment invoked but target is not assignable"};
        }
      
      virtual void
      moveInto (I&)  override
        {
          throw error::Logic{"Assignment invoked but target is not assignable"};
        }
    };
  
  
  template<class I, class D, class B =I>
  class MoveSupport
    : public NoCopyMoveSupport<I,D,B>
    {
    public:
      virtual void
      copyInto (void*)  const override
        {
          throw error::Logic{"Copy construction invoked but target allows only move construction"};
        }
      
      virtual void
      moveInto (void* targetStorage)  override
        {
          D& src = static_cast<D&> (*this);
          new(targetStorage) D(move(src));
        }
      
      // irrelevant for any practical usage, but formally required
      using NoCopyMoveSupport<I,D,B>::copyInto;
      using NoCopyMoveSupport<I,D,B>::moveInto;
    };
  
  
  template<class I, class D, class B =I>
  class CloneSupport
    : public MoveSupport<I,D,B>
    {
    public:
      virtual void
      copyInto (void* targetStorage)  const override
        {
          D const& src = static_cast<D const&> (*this);
          new(targetStorage) D(src);
        }
      
      using MoveSupport<I,D,B>::copyInto;
    };
  
  
  template<class I, class D, class B =I>
  class FullCopySupport
    : public CloneSupport<I,D,B>
    {
    public:
      virtual void
      copyInto (I& target)  const override
        {
          D&       t = D::downcast(target);
          D const& s = static_cast<D const&> (*this);
          t = s;
        }
      
      virtual void
      moveInto (I& target)  override
        {
          D& t = D::downcast(target);
          D& s = static_cast<D&> (*this);
          t = move(s);
        }
      
      using CloneSupport<I,D,B>::copyInto;
      using CloneSupport<I,D,B>::moveInto;
    };                         // see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109740
                              //  In our case here, calls will always be through VirtualCopySupportInterface
                             //   and void* is incompatible with I&, so the warning is irrelevant...
  
  
  
  namespace { // helpers to select suitable variant of copy support...
    
    template<class X>
    struct supports_only_move
      : __and_<is_move_constructible<X>
              ,__not_<is_copy_constructible<X>>
              ,__not_<is_copy_assignable<X>>
              >
      { };
    
    template<class X>
    struct supports_cloning
      : __and_<is_move_constructible<X>
              ,is_copy_constructible<X>
              ,__not_<is_copy_assignable<X>>
              >
      { };
    
    template<class X>
    struct supports_copy_and_assignment
      : __and_<is_move_constructible<X>
              ,is_copy_constructible<X>
              ,is_copy_assignable<X>
              >
      { };
  }
  
  
  
  
  template<class X, class SEL=void>
  struct CopySupport
    {
      template<class I, class D, class B =I>
      using Policy = NoCopyMoveSupport<I,D,B>;
    };
  
  template<class X>
  struct CopySupport<X,              enable_if<supports_only_move<X>> >
    {
      template<class I, class D, class B =I>
      using Policy = MoveSupport<I,D,B>;
    };
  
  template<class X>
  struct CopySupport<X,              enable_if<supports_cloning<X>> >
    {
      template<class I, class D, class B =I>
      using Policy = CloneSupport<I,D,B>;
    };
  
  template<class X>
  struct CopySupport<X,              enable_if<supports_copy_and_assignment<X>> >
    {
      template<class I, class D, class B =I>
      using Policy = FullCopySupport<I,D,B>;
    };
  
  
  
  
}} // namespace lib::meta
#endif /*LIB_META_VIRTUAL_COPY_SUPPORT_H*/