id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
5172	Boost Optional enhancement	nn-mail@…	Fernando Cacciola	"Boost.Optional is a very handy class.[[BR]]
It can be extended to allow more flexibility.
[[BR]]
Proposal:[[BR]]
Add additional argument with size to optional.[[BR]]
Then the storage is created with the given size without checking sizeof(T).[[BR]]
And only in the construct function the size is being checked.[[BR]]
If the size is less than sizeof(T) , give error.[[BR]]
If the size is much more, give a warning. [[BR]]
(say 3 times or depending on the given size, e.g. for 1-2: 32 times, for 3-16: 8 times, for 17-32: 4 times, for 33-infinite: 3 times..)[[BR]]
[[BR]]

So we can have this code:
{{{
#!cpp
#include <boost/optional2.hpp>
#include <boost/utility/in_place_factory.hpp>

class x; // Class declaration, Incomplete type!
class y; // Class declaration, Incomplete type!
class z { public: z(char) {} }; // Full type

class a
{
public:
    a();
    ~a();

    boost::optional2<x, 10> x_; // incomplete type
    boost::optional2<y, 20> y_; // incomplete type
    boost::optional2<z>     z_; // sizeof(T) like in old boost::optional
};

class x { public: x(int) {} };
class y { public: y(double) {} char c[5]; };

a::a()
{
        // Call constructors in lazy way
    x_ = boost::in_place(1);  
    y_ = boost::in_place(2.0);
    z_ = boost::in_place('c');
}

a::~a() {}

int main()
{
}
}}}

Full code resides here:[[BR]]
http://pastebin.com/4db0RFC8 [[BR]]
http://ideone.com/mBFVi [[BR]]
[[BR]]
In short, it just adds std::size_t N to the optional.
And then chooses the right size in aligned_storage.

{{{
#!cpp

template <class T, std::size_t N>
class aligned_storage
{
	// Borland ICEs if unnamed unions are used for this!
	union dummy_u_helper
	{
		char data[ N ];
	} dummy_helper ;

	union dummy_u
	{
		char data[ N ];
		BOOST_DEDUCED_TYPENAME type_with_alignment<
			::boost::alignment_of<dummy_u_helper>::value >::type aligner_;
	} dummy_ ;

				

public:

	void const* address() const { return &dummy_.data[0]; }
	void      * address()       { return &dummy_.data[0]; }
} ;

template <class T>
class aligned_storage<T, 0>
{
	// Borland ICEs if unnamed unions are used for this!
	union dummy_u
	{
		char data[ sizeof(T) ];
			BOOST_DEDUCED_TYPENAME type_with_alignment<
				::boost::alignment_of<T>::value >::type aligner_;
	} dummy_ ;


public:

	void const* address() const { return &dummy_.data[0]; }
	void      * address()       { return &dummy_.data[0]; }
} ;
}}}


I have not added check in the link above but it is easy to add it using BOOST_STATIC_ASSERT and BOOST_STATIC_WARNING (which resides in boost/serialization/static_warning.hpp)

Thanks !"	Feature Requests	closed	To Be Determined	optional	Boost Development Trunk	Optimization	invalid