Re: [boost] [config] Positive feature macros, r2

On Jan 25, 2018, at 11:39 AM, Peter Dimov via Boost wrote:

Steven Watanabe wrote:

...

I'm opposed to this, as I believe that it simply creates pointless churn. I consider the proposed benefits to be utterly insignificant.

It does not bother you that when adding a feature macro one needs to remember to add it to all compiler configurations, live or dead? And that if one forgets nobody is any the wiser?

It does not bother you that we can't just add

#if defined(__cpp_foo) && __cpp_foo >= 201400 # define BOOST_CXX14_FOO #endif

in one place and have it mostly work, instead of touching O(N) files?

I think it would be better to define the positive macros like this: #ifndef BOOST_CXX14_FOO #if defined(__cpp_foo) && __cpp_foo >= 201400 # define BOOST_CXX14_FOO 1 #else # define BOOST_CXX14_FOO 0 #endif #endif This way: - We get a warning when checking the macro when it hasn’t been defined properly - The user can easily override the value with `-DBOOST_CXX14_FOO=0` during compilation because a feature turns out to be buggy.