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Subject: Re: [boost] Is there any interest in Boost.Conversion?
From: Jeffrey Lee Hellrung, Jr. (jhellrung_at_[hidden])
Date: 2010-05-28 11:08:41

On 5/28/2010 5:23 AM, vicente.botet wrote:
> Hi,
> The Boost.Conversion library (Generic explicit conversion between unrelated types) has not revealed too much interest for the Boost community since v0.4 was released on 10/09.
> For those that don't know it yet you can get the documentation and download links from
> I have added on the sandbox some pending issues that Jeffrey Hellrung related to conversions that need extra information.
> If B1 is covertible to A1 using convert_to, now we can conver vectors of conversible types.
> B1 b10, b11, b12, b13;
> std::vector<B1> vb2;
> vb2[0]=b10;
> vb2[1]=b11;
> vb2[2]=b12;
> vb2[3]=b13;
> std::vector<A1> va2(boost::convert_to<std::vector<A1> >(vb2))
> std::vector<A1,std::allocator<A1> > va6(
> boost::convert_to<std::vector<A1,std::allocator<A1> > >(pack(vb2, std::allocator<A1>())));
> Note that when the Target constructor has some arguments (as is the case for vector with a specific allocator) we pack the Source and the Target arguments in a pack. The first argument is the Source.
> boost::conversion::pack(vb2, std::allocator<A1>())
> The function 'pack' is currently a little bit rudimentary, but is usable already for vector conversions using a specific allocator. Currently accepts only two parameters, I plan to go up to 5 parameters. Any suggestion for better namming 'boost::conversion::pack'.
> I have no solution for the ambiguity problem of a user getting two different overloads of the same conversion on different namespaces, other than suggesting that convert_to overloadings should be done on the namespace of the Source, for example.
> Jeffrey does this answer to your attends?
> I will release the pack function and vector conversion (v.0.5) on the Vault once I will update the documentation.
> Comments are welcome :)
> Best,
> _____________________
> Vicente Juan Botet Escribá

I'll have to take a look at this later. Note that in the application
where I might've used a Conversion library, I now just use a
user-provided function object to define the conversions involved, which
works well for my purposes.

As far as the ambiguity problem, I've tried using the following
framework. Essentially, you want to be able to customize the behavior
of convert_to(From&, type_tag<To>) via ADL. What you could do is first
call convert_to0 unqualified, with the convention that this would be
specialized in From's namespace. The default behavior is then to call
convert_to1 unqualified, with the convention that this would be
specialized in To's namespace. Perhaps you can rename convert_to0 and
convert_to1 to convert_to_from and convert_to_to, or something. This
might resolve the ambiguity issues, at least to a sufficient degree...

- Jeff

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