/src/poco/Foundation/include/Poco/Any.h

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//
// Any.h
//
// Library: Foundation
// Package: Core
// Module:  Any
//
// Copyright Kevlin Henney, 2000, 2001, 2002. All rights reserved.
// Extracted from Boost 1.33.1 lib and adapted for poco: Peter Schojer/AppliedInformatics 2006-02-02
//
// SPDX-License-Identifier: BSL-1.0
//


#ifndef Foundation_Any_INCLUDED
#define Foundation_Any_INCLUDED


#include "Poco/Exception.h"
#include "Poco/MetaProgramming.h"
#include <algorithm>
#include <typeinfo>
#include <cstring>
#include <cstddef>


#define poco_any_assert(cond) do { if (!(cond)) std::abort(); } while (0)


namespace Poco {

class Any;

namespace Dynamic {

class Var;
class VarHolder;
template <class T> class VarHolderImpl;

}


template <class T, std::size_t S>
struct TypeSizeLE:
  std::integral_constant<bool, (sizeof(T) <= S)>{};


template <class T, std::size_t S>
struct TypeSizeGT:
  std::integral_constant<bool, (sizeof(T) > S)>{};


template <typename PlaceholderT, unsigned int SizeV = POCO_SMALL_OBJECT_SIZE>
union Placeholder
  /// ValueHolder union (used by Poco::Any and Poco::Dynamic::Var for small
  /// object optimization, when enabled).
  ///
  /// If Holder<Type> fits into POCO_SMALL_OBJECT_SIZE bytes of storage,
  /// it will be placement-new-allocated into the local buffer
  /// (i.e. there will be no heap-allocation). The local buffer size is one byte
  /// larger - [POCO_SMALL_OBJECT_SIZE + 1], additional byte value indicating
  /// where the object was allocated (0 => heap, 1 => local).
  ///
  /// Important: for SOO builds, only same-type (or trivial both-empty no-op)
  /// swap operation is allowed.
{
public:
  struct Size
  {
    enum { value = SizeV };
  };

  Placeholder(const Placeholder&) = delete;
  Placeholder(Placeholder&&) = delete;
  Placeholder& operator=(const Placeholder&) = delete;
  Placeholder& operator=(Placeholder&&) = delete;

#ifndef POCO_NO_SOO

  Placeholder(): pHolder(0)
  {
    std::memset(holder, 0, sizeof(Placeholder));
  }

  ~Placeholder()
  {
    destruct(false);
  }

  void swap(Placeholder& other) noexcept
  {
    if (!isEmpty() || !other.isEmpty())
      std::swap(holder, other.holder);
  }

  void erase()
  {
    destruct(true);
  }

  bool isEmpty() const
  {
    static char buf[SizeV+1] = {};
    return 0 == std::memcmp(holder, buf, SizeV+1);
  }

  bool isLocal() const
  {
    return holder[SizeV] != 0;
  }

  template<typename T, typename V,
    typename std::enable_if<TypeSizeLE<T, Placeholder::Size::value>::value>::type* = nullptr>
  PlaceholderT* assign(const V& value)
  {
    erase();
    new (reinterpret_cast<PlaceholderT*>(holder)) T(value);
    setLocal(true);
    return reinterpret_cast<PlaceholderT*>(holder);
  }

  template<typename T, typename V,
    typename std::enable_if<TypeSizeGT<T, Placeholder::Size::value>::value>::type* = nullptr>
  PlaceholderT* assign(const V& value)
  {
    erase();
    pHolder = new T(value);
    setLocal(false);
    return pHolder;
  }

  PlaceholderT* content() const
  {
    if (isLocal())
      return reinterpret_cast<PlaceholderT*>(holder);
    else
      return pHolder;
  }

private:
  typedef std::max_align_t AlignerType;
  static_assert(sizeof(AlignerType) <= SizeV + 1, "Aligner type is bigger than the actual storage, so SizeV should be made bigger otherwise you simply waste unused memory.");

  void setLocal(bool local) const
  {
    holder[SizeV] = local ? 1 : 0;
  }

  void destruct(bool clear)
  {
    if (!isEmpty())
    {
      if (!isLocal())
        delete pHolder;
      else
        reinterpret_cast<PlaceholderT*>(holder)->~PlaceholderT();

      if (clear) std::memset(holder, 0, sizeof(Placeholder));
    }
  }

  mutable unsigned char holder[SizeV+1];
  AlignerType           aligner;

#else // POCO_NO_SOO

  Placeholder(): pHolder(0)
  {
  }

  ~Placeholder()
  {
    delete pHolder;
  }

  void swap(Placeholder& other) noexcept
  {
    std::swap(pHolder, other.pHolder);
  }

  void erase()
  {
    delete pHolder;
    pHolder = 0;
  }

  bool isEmpty() const
  {
    return 0 == pHolder;
  }

  bool isLocal() const
  {
    return false;
  }

  template <typename T, typename V>
  PlaceholderT* assign(const V& value)
  {
    erase();
    return pHolder = new T(value);
  }

  PlaceholderT* content() const
  {
    return pHolder;
  }

private:
#endif // POCO_NO_SOO
  PlaceholderT* pHolder;
};


class Any
  /// Any class represents a general type and is capable of storing any type, supporting type-safe extraction
  /// of the internally stored data.
  ///
  /// Code taken from the Boost 1.33.1 library. Original copyright by Kevlin Henney. Modified for Poco
  /// by Applied Informatics.
  ///
  /// Modified for small object optimization support (optionally supported through conditional compilation)
  /// by Alex Fabijanic.
{
public:

  Any()
    /// Creates an empty any type.
  {
  }

  template<typename ValueType>
  Any(const ValueType & value)
    /// Creates an any which stores the init parameter inside.
    ///
    /// Example:
    ///   Any a(13);
    ///   Any a(string("12345"));
  {
    construct(value);
  }

  Any(const Any& other)
    /// Copy constructor, works with both empty and initialized Any values.
  {
    if ((this != &other) && !other.empty())
      construct(other);
  }

  ~Any()
    /// Destructor. If Any is locally held, calls ValueHolder destructor;
    /// otherwise, deletes the placeholder from the heap.
  {
  }

  Any& swap(Any& other) noexcept
    /// Swaps the content of the two Anys.
    ///
    /// If an exception occurs during swapping, the program
    /// execution is aborted.
  {
    if (this == &other) return *this;

    if (!_valueHolder.isLocal() && !other._valueHolder.isLocal())
    {
      _valueHolder.swap(other._valueHolder);
    }
    else
    {
      try
      {
        Any tmp(*this);
        construct(other);
        other = tmp;
      }
      catch (...)
      {
        std::abort();
      }
    }

    return *this;
  }

  template<typename ValueType>
  Any& operator = (const ValueType& rhs)
    /// Assignment operator for all types != Any.
    ///
    /// Example:
    ///   Any a = 13;
    ///   Any a = string("12345");
  {
    construct(rhs);
    return *this;
  }

  Any& operator = (const Any& rhs)
    /// Assignment operator for Any.
  {
    if ((this != &rhs) && !rhs.empty())
      construct(rhs);
    else if ((this != &rhs) && rhs.empty())
      _valueHolder.erase();

    return *this;
  }

  bool empty() const
    /// Returns true if the Any is empty.
  {
    return _valueHolder.isEmpty();
  }

  const std::type_info& type() const
    /// Returns the type information of the stored content.
    /// If the Any is empty typeid(void) is returned.
    /// It is recommended to always query an Any for its type info before
    /// trying to extract data via an AnyCast/RefAnyCast.
  {
    return empty() ? typeid(void) : content()->type();
  }

  bool local() const
    /// Returns true if data is held locally (ie. not allocated on the heap).
    /// If POCO_NO_SOO is defined, it always return false.
    /// The main purpose of this function is use for testing.
  {
    return _valueHolder.isLocal();
  }

private:
  class ValueHolder
  {
  public:
    virtual ~ValueHolder() = default;

    virtual const std::type_info & type() const = 0;
    virtual void clone(Placeholder<ValueHolder>*) const = 0;
  };

  template<typename ValueType>
  class Holder : public ValueHolder
  {
  public:
    Holder(const ValueType & value) : _held(value)
    {
    }

    virtual const std::type_info& type() const
    {
      return typeid(ValueType);
    }

    virtual void clone(Placeholder<ValueHolder>* pPlaceholder) const
    {
      pPlaceholder->assign<Holder<ValueType>, ValueType>(_held);
    }

    ValueType _held;

  private:

    Holder & operator = (const Holder &);
  };

  ValueHolder* content() const
  {
    return _valueHolder.content();
  }

  template<typename ValueType>
  void construct(const ValueType& value)
  {
    _valueHolder.assign<Holder<ValueType>, ValueType>(value);
  }

  void construct(const Any& other)
  {
    if (!other.empty())
      other.content()->clone(&_valueHolder);
    else
      _valueHolder.erase();
  }

  Placeholder<ValueHolder> _valueHolder;

  template <typename ValueType>
  friend ValueType* AnyCast(Any*);

  template <typename ValueType>
  friend ValueType* UnsafeAnyCast(Any*);

  template <typename ValueType>
  friend const ValueType& RefAnyCast(const Any&);

  template <typename ValueType>
  friend ValueType& RefAnyCast(Any&);

  template <typename ValueType>
  friend ValueType AnyCast(Any&);
};


template <typename ValueType>
ValueType* AnyCast(Any* operand)
  /// AnyCast operator used to extract the ValueType from an Any*. Will return a pointer
  /// to the stored value.
  ///
  /// Example Usage:
  ///  MyType* pTmp = AnyCast<MyType*>(pAny).
  /// Will return NULL if the cast fails, i.e. types don't match.
{
  return operand && operand->type() == typeid(ValueType)
        ? &static_cast<Any::Holder<ValueType>*>(operand->content())->_held
        : 0;
}


template <typename ValueType>
const ValueType* AnyCast(const Any* operand)
  /// AnyCast operator used to extract a const ValueType pointer from an const Any*. Will return a const pointer
  /// to the stored value.
  ///
  /// Example Usage:
  ///  const MyType* pTmp = AnyCast<MyType*>(pAny).
  /// Will return NULL if the cast fails, i.e. types don't match.
{
  return AnyCast<ValueType>(const_cast<Any*>(operand));
}


template <typename ValueType>
ValueType AnyCast(Any& operand)
  /// AnyCast operator used to extract a copy of the ValueType from an Any&.
  ///
  /// Example Usage:
  ///  MyType tmp = AnyCast<MyType>(anAny).
  /// Will throw a BadCastException if the cast fails.
  /// Do not use an AnyCast in combination with references, i.e. MyType& tmp = ... or const MyType& tmp = ...
  /// Some compilers will accept this code although a copy is returned. Use the RefAnyCast in
  /// these cases.
{
  typedef typename TypeWrapper<ValueType>::TYPE NonRef;

  NonRef* result = AnyCast<NonRef>(&operand);
  if (!result)
  {
    std::string s = "RefAnyCast: Failed to convert between Any types ";
    if (operand.content())
    {
      s.append(1, '(');
      s.append(operand.content()->type().name());
      s.append(" => ");
      s.append(typeid(ValueType).name());
      s.append(1, ')');
    }
    throw BadCastException(s);
  }
  return *result;
}


template <typename ValueType>
ValueType AnyCast(const Any& operand)
  /// AnyCast operator used to extract a copy of the ValueType from an const Any&.
  ///
  /// Example Usage:
  ///  MyType tmp = AnyCast<MyType>(anAny).
  /// Will throw a BadCastException if the cast fails.
  /// Do not use an AnyCast in combination with references, i.e. MyType& tmp = ... or const MyType& = ...
  /// Some compilers will accept this code although a copy is returned. Use the RefAnyCast in
  /// these cases.
{
  typedef typename TypeWrapper<ValueType>::TYPE NonRef;

  return AnyCast<NonRef&>(const_cast<Any&>(operand));
}


template <typename ValueType>
const ValueType& RefAnyCast(const Any & operand)
  /// AnyCast operator used to return a const reference to the internal data.
  ///
  /// Example Usage:
  ///  const MyType& tmp = RefAnyCast<MyType>(anAny);
{
  ValueType* result = AnyCast<ValueType>(const_cast<Any*>(&operand));
  if (!result)
  {
    std::string s = "RefAnyCast: Failed to convert between Any types ";
    if (operand.content())
    {
      s.append(1, '(');
      s.append(operand.content()->type().name());
      s.append(" => ");
      s.append(typeid(ValueType).name());
      s.append(1, ')');
    }
    throw BadCastException(s);
  }
  return *result;
}


template <typename ValueType>
ValueType& RefAnyCast(Any& operand)
  /// AnyCast operator used to return a reference to the internal data.
  ///
  /// Example Usage:
  ///  MyType& tmp = RefAnyCast<MyType>(anAny);
{
  ValueType* result = AnyCast<ValueType>(&operand);
  if (!result)
  {
    std::string s = "RefAnyCast: Failed to convert between Any types ";
    if (operand.content())
    {
      s.append(1, '(');
      s.append(operand.content()->type().name());
      s.append(" => ");
      s.append(typeid(ValueType).name());
      s.append(1, ')');
    }
    throw BadCastException(s);
  }
  return *result;
}


template <typename ValueType>
ValueType* UnsafeAnyCast(Any* operand)
  /// The "unsafe" versions of AnyCast are not part of the
  /// public interface and may be removed at any time. They are
  /// required where we know what type is stored in the any and can't
  /// use typeid() comparison, e.g., when our types may travel across
  /// different shared libraries.
{
  return &static_cast<Any::Holder<ValueType>*>(operand->content())->_held;
}


template <typename ValueType>
const ValueType* UnsafeAnyCast(const Any* operand)
  /// The "unsafe" versions of AnyCast are not part of the
  /// public interface and may be removed at any time. They are
  /// required where we know what type is stored in the any and can't
  /// use typeid() comparison, e.g., when our types may travel across
  /// different shared libraries.
{
  return AnyCast<ValueType>(const_cast<Any*>(operand));
}


} // namespace Poco


#endif

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Created: 2023-12-20 07:15