Re: [boost] [result_of] Make `cpp0x_result_of_impl` public

Subject: Re: [boost] [result_of] Make `cpp0x_result_of_impl` public
From: Daniel Walker (daniel.j.walker_at_[hidden])
Date: 2012-03-27 14:49:06

On Mar 27, 2012, at 1:35 PM, Eric Niebler wrote:

> On 3/24/2012 1:52 AM, Michel Morin wrote:
>> There are two implementations of boost::result_of: a TR1-style
>> implementation and a decltype-based implementation. While
>> the TR1-style implementation has a public interface `boost::tr1_result_of`,
>> decltype-based one doesn't have a public interface.
> 
> Yes, I'm the one responsible for this change.
> 
>> By defining BOOST_RESULT_OF_USE_DECLTYPE,
>> boost::result_of use decltype-based implementation.
>> But this is not always a viable solution, since this breaks
>> some Boost libraries.
>> 
>> So how about adding `boost::cxx11_result_of` as public interface
>> of the decltype-based implementation?
>> Attached a patch to add `boost::cxx11_result_of`.
>> (This patch also changes the name of `cpp0x_result_of_impl`
>> to `cxx11_result_of_impl` to reflect the recent discussion on
>> the cpp/cxx naming.)
> 
> The patch looks fine, and I guess I'm as qualified to apply it as
> anybody. But it doesn't have docs and tests. Care to address that? The
> docs probably only need a line or two, and you can copy the tests for
> tr1_result_of.
> 

I'm not sure that I agree that cxx11_result_of is a good idea. The plan was for boost::result_of to become a C++11 result_of as soon as we're comfortable flicking the switch so that it's on by default (on platforms that can support it). Michel, do you just want a C++11 result_of that works out-of-the-box or do you really need a separate interface in addition to boost::result_of?

>> P.S.
>> Is it worth trying to use this `boost::cxx11_result_of`
>> in `boost::transform_iterator` code on trunk?
> 
> Now that we have a macro to detect compliance with N3256, we have a way
> to safely enable decltype-based result_of by default. We should think
> about doing that and fixing the bugs this will flush out. This should be
> a separate step, though, and it should be done very early in a release
> cycle.

Good idea.

- Daniel