action-container.h

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////////////////////////////////////////////////////////////////////////
//
// Copyright (C) 1993-2022 The Octave Project Developers
//
// See the file COPYRIGHT.md in the top-level directory of this
// distribution or <https://octave.org/copyright/>.
//
// This file is part of Octave.
//
// Octave 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 3 of the License, or
// (at your option) any later version.
//
// Octave 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
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Octave; see the file COPYING.  If not, see
// <https://www.gnu.org/licenses/>.
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////////////////////////////////////////////////////////////////////////
 
#if ! defined (octave_action_container_h)
#define octave_action_container_h 1
 
#include "octave-config.h"
 
#include <cstddef>
#include <functional>
 
// This class allows registering actions in a list for later
// execution, either explicitly or when the container goes out of
// scope.
 
// FIXME: is there a better name for this class?
 
namespace octave
{
  class
  action_container
  {
  public:
 
    // A generic unwind_protect element.  Knows how to run itself and
    // discard itself.  Also, contains a pointer to the next element.
    class elem
    {
    public:
 
      friend class action_container;
 
      elem (void) { }
 
      // No copying!
 
      elem (const elem&) = delete;
 
      elem& operator = (const elem&) = delete;
 
      virtual ~elem (void) = default;
 
      virtual void run (void) { }
    };
 
    // An element that merely runs a void (*)(void) function.
 
    class fcn_elem : public elem
    {
    public:
 
      // FIXME: Do we need to apply std::forward to the arguments to
      // std::bind here?
 
      template <typename F, typename... Args>
      fcn_elem (F&& fcn, Args&&... args)
        : m_fcn (std::bind (fcn, args...))
      { }
 
      void run (void) { m_fcn (); }
 
    private:
 
      std::function<void (void)> m_fcn;
    };
 
    // An element that stores arbitrary variable, and restores it.
 
    template <typename T>
    class restore_var_elem : public elem
    {
    public:
 
      restore_var_elem (T& ref, const T& val)
        : m_ptr (&ref), m_val (val) { }
 
      // No copying!
 
      restore_var_elem (const restore_var_elem&) = delete;
 
      restore_var_elem& operator = (const restore_var_elem&) = delete;
 
      void run (void) { *m_ptr = m_val; }
 
    private:
 
      T *m_ptr, m_val;
    };
 
    // Deletes a class allocated using new.
 
    template <typename T>
    class delete_ptr_elem : public elem
    {
    public:
 
      delete_ptr_elem (T *ptr)
        : m_ptr (ptr) { }
 
      // No copying!
 
      delete_ptr_elem (const delete_ptr_elem&) = delete;
 
      delete_ptr_elem operator = (const delete_ptr_elem&) = delete;
 
      void run (void) { delete m_ptr; }
 
    private:
 
      T *m_ptr;
    };
 
    action_container (void) { }
 
    // No copying!
 
    action_container (const action_container&) = delete;
 
    action_container& operator = (const action_container&) = delete;
 
    virtual ~action_container (void) = default;
 
    template <typename F, typename... Args>
    void add (F&& fcn, Args&&... args)
    {
      add_action (new fcn_elem (std::forward<F> (fcn),
                                std::forward<Args> (args)...));
    }
 
    // Use separate template types for function pointer parameter
    // declarations and captured arguments so that differences in
    // const are handled properly.
 
    template <typename... Params, typename... Args>
    void add_fcn (void (*fcn) (Params...), Args&&... args)
    {
      add_action (new fcn_elem (fcn, std::forward<Args> (args)...));
    }
 
    template <typename T, typename... Params, typename... Args>
    void add_method (T *obj, void (T::*method) (Params...), Args&&... args)
    {
      add_action (new fcn_elem (method, obj, std::forward<Args> (args)...));
    }
 
    template <typename T, typename... Params, typename... Args>
    void add_method (T& obj, void (T::*method) (Params...), Args&&... args)
    {
      add_action (new fcn_elem (method, &obj, std::forward<Args> (args)...));
    }
 
    // Call to delete (T*).
 
    template <typename T>
    void add_delete (T *obj)
    {
      add_action (new delete_ptr_elem<T> (obj));
    }
 
    // Protect any variable.
    template <typename T>
    void protect_var (T& var)
    {
      add_action (new restore_var_elem<T> (var, var));
    }
 
    // Protect any variable, value given.
    template <typename T>
    void protect_var (T& var, const T& val)
    {
      add_action (new restore_var_elem<T> (var, val));
    }
 
    operator bool (void) const { return ! empty (); }
 
    virtual void run_first (void) = 0;
 
    OCTAVE_API void run (std::size_t num);
 
    void run (void) { run (size ()); }
 
    virtual void discard_first (void) = 0;
 
    void discard (std::size_t num)
    {
      if (num > size ())
        num = size ();
 
      for (std::size_t i = 0; i < num; i++)
        discard_first ();
    }
 
    void discard (void) { discard (size ()); }
 
    virtual std::size_t size (void) const = 0;
 
    bool empty (void) const { return size () == 0; }
 
  protected:
 
    virtual void add_action (elem *new_elem) = 0;
  };
}
 
#endif