[boost] Re: Formal Review Request: class optional<>

[Vincent Finn]

Hi,

I have one comment and one question.
So first the comment

I was recently thinking about a similar thing for a slightly different purpose. You seem to concentrate on option return values, what about optional arguments.

e.g.
void fn(int iImportant, optional<int> iNotImportant = optional<int>());

The reasoning for this is similar to for the return
the function could tell if the user had passed in an argument and act accordingly

Normally you can have a special default value but cases can occur where and int is valid but none might be required.

The reason I assume you don't allow for this is that your constructor is explicit and for easier calling sytax in this case that would not be best (I think)
i.e. I would want to be able to call the above as
fn(1, 3);

The most common reason, though, would be the desire to use references rather than pointers
int fn1(optional<int&> iMayNotWant = optional<int&>());
instead of
int fn2(int* piMayNotWant = NULL);

I assume this isn't possible since references aren't default constructable but it would be nice :-)

---

And now the question
can this be used with VC6 ?

I have tried at it won't compile (I'm compiling with boost 1.29)
I get the following error in optional

optional_detail.hpp(91) : error C2371: 'proxy' : redefinition; different basic types
optional_detail.hpp(90) : see declaration of 'proxy'
optional_detail.hpp(171) : see reference to class template instantiation 'boost::optional_detail::value_based_optional<T>' being compiled

and lots of errors in
mpl\logical\and.hpp
e.g
mpl\logical\and.hpp(115) : error C2039: 'type' : is not a member of '`global namespace''
mpl\logical\and.hpp(115) : error C2146: syntax error : missing ',' before identifier 'value'

and a lot more :-(

Vin



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