/* | |
Copyright 2005-2007 Adobe Systems Incorporated | |
Use, modification and distribution are subject to the Boost Software License, | |
Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at | |
http://www.boost.org/LICENSE_1_0.txt). | |
See http://opensource.adobe.com/gil for most recent version including documentation. | |
*/ | |
/*************************************************************************************************/ | |
#ifndef GIL_DYNAMICIMAGE_VARIANT_HPP | |
#define GIL_DYNAMICIMAGE_VARIANT_HPP | |
//////////////////////////////////////////////////////////////////////////////////////// | |
/// \file | |
/// \brief Support for run-time instantiated types | |
/// \author Lubomir Bourdev and Hailin Jin \n | |
/// Adobe Systems Incorporated | |
/// \date 2005-2007 \n Last updated on September 18, 2007 | |
/// | |
//////////////////////////////////////////////////////////////////////////////////////// | |
#include "../../gil_config.hpp" | |
#include "../../utilities.hpp" | |
#include <cstddef> | |
#include <cassert> | |
#include <algorithm> | |
#include <typeinfo> | |
#include <boost/bind.hpp> | |
#include <boost/mpl/transform.hpp> | |
#include <boost/mpl/size.hpp> | |
#include <boost/mpl/sizeof.hpp> | |
#include <boost/mpl/max.hpp> | |
#include <boost/mpl/at.hpp> | |
#include <boost/mpl/fold.hpp> | |
namespace boost { namespace gil { | |
namespace detail { | |
template <typename Types, typename T> struct type_to_index; | |
template <typename Op, typename T> struct reduce; | |
struct destructor_op { | |
typedef void result_type; | |
template <typename T> result_type operator()(const T& t) const { t.~T(); } | |
}; | |
template <typename T, typename Bits> void copy_construct_in_place(const T& t, Bits& bits); | |
template <typename Bits> struct copy_construct_in_place_fn; | |
} | |
/** | |
\brief Represents a concrete instance of a run-time specified type from a set of types | |
\class variant | |
\ingroup Variant | |
A concept is typically modeled by a collection of different types. They may be instantiations | |
of a templated type with different template parameters or even completely unrelated types. | |
We call the type with which the concept is instantiated in a given place in the code "the concrete type". | |
The concrete type must be chosen at compile time, which sometimes is a severe limitation. | |
Consider, for example, having an image concept modeled by an image class templated over the color space. | |
It would be difficult to write a function that reads an image from file preserving its native color space, since the | |
type of the return value is only available at run time. It would be difficult to store images of different color | |
spaces in the same container or apply operations on them uniformly. | |
The variant class addresses this deficiency. It allows for run-time instantiation of a class from a given set of allowed classes | |
specified at compile time. For example, the set of allowed classes may include 8-bit and 16-bit RGB and CMYK images. Such a variant | |
can be constructed with rgb8_image_t and then assigned a cmyk16_image_t. | |
The variant has a templated constructor, which allows us to construct it with any concrete type instantiation. It can also perform a generic | |
operation on the concrete type via a call to apply_operation. The operation must be provided as a function object whose application | |
operator has a single parameter which can be instantiated with any of the allowed types of the variant. | |
variant breaks down the instantiated type into a non-templated underlying base type and a unique instantiation | |
type identifier. In the most common implementation the concrete instantiation in stored 'in-place' - in 'bits_t'. | |
bits_t contains sufficient space to fit the largest of the instantiated objects. | |
GIL's variant is similar to boost::variant in spirit (hence we borrow the name from there) but it differs in several ways from the current boost | |
implementation. Most notably, it does not take a variable number of template parameters but a single parameter defining the type enumeration. As | |
such it can be used more effectively in generic code. | |
The Types parameter specifies the set of allowable types. It models MPL Random Access Container | |
*/ | |
template <typename Types> // models MPL Random Access Container | |
class variant { | |
// size in bytes of the largest type in Types | |
static const std::size_t MAX_SIZE = mpl::fold<Types, mpl::size_t<0>, mpl::max<mpl::_1, mpl::sizeof_<mpl::_2> > >::type::value; | |
static const std::size_t NUM_TYPES = mpl::size<Types>::value; | |
public: | |
typedef Types types_t; | |
typedef struct { char data[MAX_SIZE]; } base_t; // empty space equal to the size of the largest type in Types | |
// Default constructor - default construct the first type | |
variant() : _index(0) { new(&_bits) typename mpl::at_c<Types,0>::type(); } | |
virtual ~variant() { apply_operation(*this, detail::destructor_op()); } | |
// Throws std::bad_cast if T is not in Types | |
template <typename T> explicit variant(const T& obj){ _index=type_id<T>(); if (_index==NUM_TYPES) throw std::bad_cast(); detail::copy_construct_in_place(obj, _bits); } | |
// When doSwap is true, swaps obj with the contents of the variant. obj will contain default-constructed instance after the call | |
template <typename T> explicit variant(T& obj, bool do_swap); | |
template <typename T> variant& operator=(const T& obj) { variant tmp(obj); swap(*this,tmp); return *this; } | |
variant& operator=(const variant& v) { variant tmp(v ); swap(*this,tmp); return *this; } | |
variant(const variant& v) : _index(v._index) { apply_operation(v, detail::copy_construct_in_place_fn<base_t>(_bits)); } | |
template <typename T> void move_in(T& obj) { variant tmp(obj, true); swap(*this,tmp); } | |
template <typename TS> friend bool operator==(const variant<TS>& x, const variant<TS>& y); | |
template <typename TS> friend bool operator!=(const variant<TS>& x, const variant<TS>& y); | |
template <typename T> static bool has_type() { return type_id<T>()!=NUM_TYPES; } | |
template <typename T> const T& _dynamic_cast() const { if (!current_type_is<T>()) throw std::bad_cast(); return *gil_reinterpret_cast_c<const T*>(&_bits); } | |
template <typename T> T& _dynamic_cast() { if (!current_type_is<T>()) throw std::bad_cast(); return *gil_reinterpret_cast < T*>(&_bits); } | |
template <typename T> bool current_type_is() const { return type_id<T>()==_index; } | |
base_t bits() const { return _bits; } | |
std::size_t index() const { return _index; } | |
private: | |
template <typename T> static std::size_t type_id() { return detail::type_to_index<Types,T>::value; } | |
template <typename Cs> friend void swap(variant<Cs>& x, variant<Cs>& y); | |
template <typename Types2, typename UnaryOp> friend typename UnaryOp::result_type apply_operation(variant<Types2>& var, UnaryOp op); | |
template <typename Types2, typename UnaryOp> friend typename UnaryOp::result_type apply_operation(const variant<Types2>& var, UnaryOp op); | |
template <typename Types1, typename Types2, typename BinaryOp> friend typename BinaryOp::result_type apply_operation(const variant<Types1>& arg1, const variant<Types2>& arg2, BinaryOp op); | |
base_t _bits; | |
std::size_t _index; | |
}; | |
namespace detail { | |
template <typename T, typename Bits> | |
void copy_construct_in_place(const T& t, Bits& bits) { | |
T& b=*gil_reinterpret_cast<T*>(&bits); | |
new(&b)T(t); // default-construct | |
} | |
template <typename Bits> | |
struct copy_construct_in_place_fn { | |
typedef void result_type; | |
Bits& _dst; | |
copy_construct_in_place_fn(Bits& dst) : _dst(dst) {} | |
template <typename T> void operator()(const T& src) const { copy_construct_in_place(src,_dst); } | |
}; | |
template <typename Bits> | |
struct equal_to_fn { | |
const Bits& _dst; | |
equal_to_fn(const Bits& dst) : _dst(dst) {} | |
typedef bool result_type; | |
template <typename T> result_type operator()(const T& x) const { | |
return x==*gil_reinterpret_cast_c<const T*>(&_dst); | |
} | |
}; | |
} | |
// When doSwap is true, swaps obj with the contents of the variant. obj will contain default-constructed instance after the call | |
template <typename Types> | |
template <typename T> variant<Types>::variant(T& obj, bool do_swap) { | |
_index=type_id<T>(); | |
if (_index==NUM_TYPES) throw std::bad_cast(); | |
if (do_swap) { | |
new(&_bits) T(); // default construct | |
swap(obj, *gil_reinterpret_cast<T*>(&_bits)); | |
} else | |
detail::copy_construct_in_place(const_cast<const T&>(obj), _bits); | |
} | |
template <typename Types> | |
void swap(variant<Types>& x, variant<Types>& y) { | |
std::swap(x._bits,y._bits); | |
std::swap(x._index, y._index); | |
} | |
template <typename Types> | |
inline bool operator==(const variant<Types>& x, const variant<Types>& y) { | |
return x._index==y._index && apply_operation(x,detail::equal_to_fn<typename variant<Types>::base_t>(y._bits)); | |
} | |
template <typename C> | |
inline bool operator!=(const variant<C>& x, const variant<C>& y) { | |
return !(x==y); | |
} | |
} } // namespace boost::gil | |
#endif |