Re: [boost] [Config] Support for switching between std:: and boost:: equivalents.

Subject: Re: [boost] [Config] Support for switching between std:: and boost:: equivalents.
From: Edward Diener (eldiener_at_[hidden])
Date: 2015-06-05 10:42:50

On 6/5/2015 10:00 AM, Rob Stewart wrote:
> On June 5, 2015 5:30:03 AM EDT, Edward Diener <eldiener_at_[hidden]> wrote:
>> On 6/5/2015 3:41 AM, John Maddock wrote:
>>> There is a pull-request for Config to provide support for switching
>>> between boost:: and std:: library equivalents:
>>> https://github.com/boostorg/config/pull/63
>>>
>>> My questions are:
>>>
>>> * Is this the right approach?  And,
>>> * Is Boost.Config the right place for it?
>>
>> I don't know what "the right approach" would be but this is one
>> approach that does work easily.
>
> It does seem like a reasonable approach overall. It's relatively simple and doesn't try to hide much.
>
> I can't think of a better place for this than Config.
>
>> It is very easy to use. For library 'XXX':
>>
>> 1) Just include the particular Boost.config header provided for a
>> particular interoperable library XXX:
>>
>> #include <boost/config/cpp/XXX.hpp>
>
> I noticed in your PR that you also provide a header to get all such headers at once. I wonder whether the individual headers are really that useful. You could keep the implementation you have, but just document the one header.

The one header is documented. I have the individual headers to avoid 
flooding the macro namespaces with lots of macros you are not going to use.

>
>> 2) Include that library's main header file using the macro provided
>> for that library:
>>
>> #include BOOST_CPP_XXX_HDR
>
> Why do you have "CPP" in that name? BOOST_XXX_HDR would seem sufficient. I also would suggest using HEADER rather than HDR.

I like to avoid macro name clashes, Having a common prefix, such as CPP, 
tends to do that.

As far as the more verbose HEADER instead of the shorter HDR that's fine 
with me if others like that instead. I could even change 
BOOST_CPP_XXX_NS to BOOST_CPP_XXX_NAMESPACE and have everybody type out 
the fully explicit names.

>
>> 3) In code for that library's functionality use the namespace macro
>> provided for accessing the library's functionality:
>> BOOST_CPP_XXX_NS::some_functionality etc.
>
> Why do you have "CPP" in that name? BOOST_XXX_NS would seem sufficient.
>
>> If you need to do anything different depending on whether you are
>> using
>> the C++ standard version of the library or the Boost version of the
>> library you can test the BOOST_CPP_HAS_XXX macro, which is 1 for the
>> C++
>> standard version existing in the compiler implementation and is 0 for
>> only the Boost version existing in the compiler implementation.
>
> That macro would seem better named, BOOST_HAS_STD_XXX our BOOST_XXX_IS_STD. (The latter is more consistent with my earlier suggestions.)

Again I like distinct macro names so BOOST_CPP_something seems right, 
but your other suggestions, as BOOST_CPP_HAS_STD_XXX or 
BOOST_CPP_XXX_IS_STD, are fine. Please realize that all macros are in a 
global namespace with everything and avoiding macro name clashes in any 
TU is of paramount importance.