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