several.hpp

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/*
  SEVERAL.hpp  -  abstraction providing a limited fixed number of elements

   Copyright (C)
     2008,            Hermann Vosseler <Ichthyostega@web.de>
     2024,            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_SEVERAL_H
#define LIB_SEVERAL_H


#include "lib/nocopy.hpp"
#include "lib/index-iter.hpp"

#include <cstddef>
#include <functional>


namespace lib {
  
  namespace several {// Storage header implementation details
    
    template<class TAR>
    class SelfDestructor
      {
        std::function<void(TAR*)> dtor_{};
        
      public:
        template<class FUN>
        void
        installDestructor (FUN&& dtor)
          {
            dtor_ = std::forward<FUN> (dtor);
          }
        
       ~SelfDestructor()
          {
            if (isArmed())
              {
                auto destructionFun = std::move(dtor_);
                ENSURE (not dtor_);
                destructionFun (target());
              }
          }
       
        bool isArmed() const { return bool(dtor_); }
        auto getDtor() const { return dtor_;       }
        void destroy()       { target()->~TAR();   }
        TAR* target()        { return static_cast<TAR*>(this); }
      };
    
    template<class I>
    struct ArrayBucket
      : SelfDestructor<ArrayBucket<I>>
      {
        ArrayBucket (size_t storageSize, size_t buffStart, size_t elmSize = sizeof(I))
          : cnt{0}
          , spread{elmSize}
          , buffSiz{storageSize - buffStart}
          , buffOffset{buffStart}
          { }
        
        using Deleter = std::function<void(ArrayBucket*)>;
        
        size_t cnt;
        size_t spread;
        size_t buffSiz;
        size_t buffOffset;
        
        static constexpr size_t storageOffset = sizeof(ArrayBucket);
        size_t getAllocSize()  const { return buffOffset +buffSiz; }
        
        
        std::byte*
        storage()
          {
            return reinterpret_cast<std::byte*>(this) + buffOffset;
          }
        
        I&
        subscript (size_t idx)
          {
            std::byte* elm = storage() + (idx * spread);
            ENSURE (storage() <= elm and elm < storage()+buffSiz);
            return * std::launder (reinterpret_cast<I*> (elm));
          }
        
      };
    
  }//(End)implementation details
  
  
  
  /************************************************/
  template<class I>
  class Several
    : util::MoveAssign
    {
    protected:
      using Bucket = several::ArrayBucket<I>*;
      
      Bucket data_{nullptr};
      
    public:
      Several() =default; 
      
     ~Several()  noexcept
        try { if (data_) data_->destroy(); }
        ERROR_LOG_AND_IGNORE (progress, "clean-up Several data")
      
      
      Several (Several&& rr)
        {
          std::swap (data_, rr.data_);
        }
      Several& operator= (Several&& rr)
        {
          std::swap (data_, rr.data_);
          return *this;
        }
      
      size_t
      size()  const
        {
          return data_? data_->cnt : 0;
        }
      
      bool
      empty()  const
        {
          return not data_;
        }
      
      I&
      operator[] (size_t idx)
        {
          REQUIRE (data_);
          return data_->subscript (idx);
        }
      
      I const&
      operator[] (size_t idx)  const
        {
          return const_cast<Several&>(*this).operator[] (idx);
        }
      
      I& front() { return operator[] (0);                         }
      I& back()  { return operator[] (data_? data_->cnt-1 : 0);   }
      
      using iterator       = lib::IndexIter<Several>;
      using const_iterator = lib::IndexIter<const Several>;
      
      iterator begin()             { return iterator{*this};      }
      iterator end()               { return iterator{};           }
      const_iterator begin() const { return const_iterator{*this};}
      const_iterator end()   const { return const_iterator{};     }
      
      friend auto begin (Several& svl)       { return svl.begin();}
      friend auto end   (Several& svl)       { return svl.end();  }
      friend auto begin (Several const& svl) { return svl.begin();}
      friend auto end   (Several const& svl) { return svl.end();  }
      
      
    protected:
      size_t
      spread()  const
        {
          return data_? data_->spread : sizeof(I);
        }
      
      size_t
      storageBuffSiz()  const
        {
          return data_? data_->buffSiz : 0;
        }
      
      bool
      hasReserve (size_t requiredSize, size_t newElms =1)  const
        {
          if (requiredSize < spread())
            requiredSize = spread();
          size_t extraSize{requiredSize * newElms};
          if (requiredSize > spread())
            extraSize += (requiredSize - spread())*size();
          return data_
             and data_->buffSiz >= size()*spread() + extraSize;
        }
    };
  
  
} // namespace lib
#endif