Re: [boost] Re: Using variant library with Boost 1.30.0

From: Allen Bierbaum (allenb_at_[hidden])
Date: 2003-04-04 17:10:27

Eric Friedman wrote:
> Allen Bierbaum wrote:
> 
>>I have been very impressed with the Variant library and started using it
>>with Boost 1.29.
> 
> 
> Good to hear. I'd be interested in your experience using the library in a
> real-world (?) application.

I was able to get variant working with 1.30 by pulling some of the code 
out of the sandbox.

I have started using it in my application and have run into one major 
limitation: variant size  (in number of allowed types)

I need to use a variant of about 15-20 allowed types.  By default 
variant only works with 10 types.  I know that by defining:

BOOST_MPL_LIMIT_LIST_SIZE=20  and BOOST_MPL_NO_PREPROCESSED_HEADERS

I can get the limit up to 20 or 30 or whatever I want.  Unfortunately 
this also ups the limits on *all* lists that may be in the code and 
makes compile times take much longer since I can't use the preprocessed 
headers.

Anyway, looking back through the list I found a reference here:

http://lists.boost.org/MailArchives/boost/msg38637.php

that says the recommended way to do this type of thing when users want 
longer list types is to use the numbered list types.  I know this 
doesn't directly relate to variant, but I was thinking it would be very 
nice to have something similar for variant.

So for example I could say:

boost::variant27<...>

to get a variant that allows 27 types.

I would also be happy with something like:

boost::variant<27, type1, type2,..., type27>

but I could see where some people would not like this form since it 
requires the size to be explicitly set.

Maybe something like this would work better.

boost::variantS<27, type1, ..., type27>

This provides an explicit type that is used when you want the first 
parameter to be the size, but still allows the normal boost::variant 
type to automatically detect the size.

What do you think, are either of these two options feasible (or is there 
already support for it that I missed)?

-Allen

> 
> 
>>I now need to start to using Boost 1.30.0 though and I don't think the
>>variant library distributed for the review will work with the 1.30.0
>>release.
>>
>>Does anyone have any suggestions how I can use the variant library with
>>Boost 1.30.0?  Anyone have an updated distribution of the Variant library?
> 
> 
> I plan to ready the code for release with 1.31. Until then, you can try
> using the code in the sandbox, which I have recently updated to work with
> 1.30.
> 
> Note, however, that the code in the sandbox will change -- sometimes
> significantly -- and integrates variant with other libraries I am
> developing, such as Boost.Visitor and Boost.Move. If this is a problem for
> you, you may want to update the variant submission code yourself. Most of
> the required changes are to accomodate class and header name-changes in MPL
> between 1.29 and 1.30 -- nothing terribly significant.
> 
> Thanks,
> Eric
> 
> 
> 
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-- 
-- Allen Bierbaum                          allenb_at_[hidden] --
-- VR Juggler Team                               www.vrjuggler.org --
-- Virtual Reality Applications Center        www.vrac.iastate.edu --