Hi All!
I've finally finished preparing this class for formal review.
{note: with just the basic exception safety guarantees, not with the
implementation I described recently in another post)
The headers, documentation and test files are packed in:
http://groups.yahoo.com/group/boost/files/optional.zip
I hereby ask this to be scheduled for formal review.
(I will also ask for a formal review of the Numeric Conversion Library
shortly...
but I wanted to have this one scheduled first since it is significantly
smaller)
Here is a description of the submission (adapted from the docs):
An object of type optional<T> can be used
to hold a value of type T which might have
an *uninitialized* state.
It has pointer semantics in order to deal
with its possibly uninitialized state;
but it does not require any allocation
or lifetime management.
The following cases shows the intended
usage for optional<>
//
// Usage Case A:
// Functions which may not have a value to return
// but cannot treat this situation as an error.
//
optional<char> get_async_input()
{
if ( !queue.empty() )
return optional<char>(queue.top());
else return optional<char>(); // uninitialized
}
void recieve_async_message()
{
optional<char> rcv ;
while ( !!(rcv = get_async_input()) && !timeout() )
output(*rcv);
}
//
// Usage Case B:
// Local variable which is never assigned a value.
//
optional<string> name ;
if ( database.open() )
{
*name = database.lookup(employer_name);
}
else
{
if ( can_ask_user )
*name = user.ask(employer_name);
}
if ( !!name )
print(*name);
else print("employer's name not found!");
//
// Usage Case C:
// Data member which can remain uninitialized.
//
class figure
{
public:
figure()
{
// data member clipping rect is
// uninitialized at this point.
}
void clip_in_rect ( rect const& rect )
{
....
*m_clipping_rect = rect ; // initialized here.
}
// this can return NULL.
rect const* get_clipping_rect()
{ return peek(m_clipping_rect); }
private :
optional<rect> m_clipping_rect ;
};
It uses aligned_storage<>, placement new and a explicit delete as the
implementation.
It only requires T's copy-constructor. The T's default constructor is not
required nor used.
It offers only the basic exception guarantees: the optionals are reset to
uninitialized if exceptions are thrown during updating operations.
TIA,
Fernando Cacciola
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