On 2010-10-06 13:11, Stewart, Robert wrote:
What also doesn't seem right to me is that, e.g.,
struct A { int a; double b; double c; std::string d; };
struct B { boost::optional< int> a; boost::optional< double> b; boost::optional< double> c; boost::optional< std::string> d; };
the size of A is 32 bytes in this case, and the sizeof B is 56 bytes: almost doubled. So, while it may be argued that the case above is a corner case, too, I don't it's an acceptable penalty to anyone to pay 24 bytes for something that can be stored in 4 bits and/or in the type itself.
That's an interesting scenario, but is it likely that so many pieces would be optional in a single context like that?
This is likely indeed, if you're going to model message structures, the most direct representation commonly contains a great deal of optionals.
(I haven't looked, but I do hope that the bool follows the optional value to reduce padding overhead.)
It doesn't, the boolean is followed by the optional value (see boost/optional/optional.hpp lines 447-448).
I wouldn't want that to replace the current design, but it would be useful as an alternative to the current design or an extension of it.
I agree. Cheers, Rutger