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?
Thanks for your comments, John.
That is my pull request so I will comment now that you have so
graciously provided a forum for my idea.
I don't know what "the right approach" would be but this is one approach
that does work easily, following the documentation I have written about
it and added to the Boost.config documentation.
I have written and added tests for all the Boost libraries involved
which have a C++ standard version which may be interoperably used
instead of the Boost version in code. These tests I would add as PRs to
the particular libraries once this config PR is pushed to 'develop'. The
tests are largely proof of concept tests that show that code does work.
The tests are not meant to be extensive tests for each library's
functionality.
I have also used the code successfully in this PR for a library I am
developing.
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
2) Include that library's main header file using the macro provided for
that library:
#include BOOST_CPP_XXX_HDR
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.
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's it for any given library supported. You are using the C++
standard version of the library if it exists in the compiler
implementation or the Boost version of the library if it does not exists
in the compiler implementation.
The Boost implementations supported are:
array
atomic
bind
chrono
function
hash
mem_fn
random
ratio
reg/creg
regex
shared_ptr
thread
tuple
type_index
type_traits
unordered_map
unordered_multimap
unordered_set
unordered_multiset
If I have missed any Boost libraries which have a close C++ standard
equivalent just tell me and I will add it with some added tests for that
particular library.
I give a basic example how the macros are used using regex in the
documentation.
Of course there may be differences between the C++ standard library
equivalent of a Boost library and the Boost library itself. But for the
most part the system I have provided will work and when it does not work
because of differences, at the very least you can use the
BOOST_CPP_HAS_XXX form of macro to decide what you want to do.
As to whether or not it belongs in Boost.config:
1) The macros for any given library 'XXX" are not automatically brought
in by the normal 'include ', so they affect nothing in
Boost.config.
2) The system is based directly on Boost.config detection macros in
order to determine whether or not a particular 'XXX' equivalent library
exists.
3) The macros do "configure" the ability to use either a Boost library
or its C++ standard equivalent using the same syntax.
4) The system could be put in its own library with a dependency on
Boost.config only, but it is such a simple system already dependent on
Boost.config that I felt it would easily fit as part of Boost.config
than as its own separate library.
5) I wanted to push it to 'develop' and let others use it and add the
per library PR's to test it. If it was found to be flawed or could be
better in any way I could then change it on 'develop', and if people
were satisfied with it as a workable solution it could eventually be
merged to 'master'. If not it could be easily removed if necessary since
it exists in its own header files apart from the rest of Boost.config.
Even its documentation is a separate Boost.config .qbk file.
I know these macros work and provide an easy transition between using
the C++ standard equivalent of a Boost library if it exists in a
compiler implementation or the Boost version if it does not. I made no
attempt to create a per XXX library bridge between functionality of the
C++ standard equivalent of a Boost library and the Boost library itself
when the functionality differs because one has functionality that the
other does not or, in the rarer case, when the same syntactical
functionality works differently. I feel that such an attempt at
interoperability is outside the purpose of the system I provide. For
many of the mainstream Boost libraries which are now in the C++11
standard as libraries the system I have created, via macros, of
including the correct header and use the correct namespace works largely
flawlessly without having to consider differences. I am thinking of such
closely equivalent and highly used libraries as 'function', 'bind',
'ref/cref', 'regex' etc. The system I have provided is meant to make
writing code much easier without having to worry about which library I
am using, the C++ standard version or the Boost version.
If there are better interoperable systems I would love to hear about
them. But for me personally any system where I have to jump through
hoops simply to be able to write code which works whether I am using a
Boost library or its C++ standard library equivalent, will not be worth it.
The fork of config on which this PR is based is under my own account at
https://github.com/eldiener/config.git if anyone wants to play around
with it. The documentation I added to the Boost.config docs explain
everything better than I have here. I am of course willing to support
this work. My local tests I can push to forks of each XXX Boost library
supported by these macros, since I have already made local branches for
each XXX library with tests added for these Boost.config macros to show
that they work.
Questions, concerns etc are welcome.
