Boost C++ Libraries

optional<char> get_async_input()
{
    if ( !queue.empty() )
        return optional<char>(queue.top());
    else return optional<char>(); // uninitialized
}

void receive_async_message()
{
    optional<char> rcv ;
    // The safe boolean conversion from 'rcv' is used here.
    while ( (rcv = get_async_input()) && !timeout() )
        output(*rcv);
}

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!");

class figure
{
    public:

    figure()
    {
        // data member 'm_clipping_rect' is uninitialized at this point.
    }

    void clip_in_rect ( rect const& rect )
    {
        ....
        m_clipping_rect = rect ; // initialized here.
    }

    void draw ( canvas& cvs )
    {
        if ( m_clipping_rect )
            do_clipping(*m_clipping_rect);

        cvs.drawXXX(..);
    }

    // this can return NULL.
    rect const* get_clipping_rect() { return get_pointer(m_clipping_rect); }

    private :

    optional<rect> m_clipping_rect ;

};

class ExpensiveCtor { ... } ;
class Fred
{
    Fred() : mLargeVector(10000) {}

    std::vector< optional<ExpensiveCtor> > mLargeVector ;
} ;