[cfe-dev] [libcxx] using has_extension instead of has_feature

[Howard Hinnant]

On Aug 12, 2011, at 5:25 AM, Jean-Daniel Dupas wrote:

> Hello,
> 
> I'd like to propose to use __has_extension instead of __has_feature to detect available features in libc++ headers.
> 
> Using __has_feature prevent usage of functionalities provided by clang as extension when compiling in older standard mode.
> 
> As __has_extension is a superset of __has_feature, it should not have any effect on people using the library in c++0x mode.
> 
> And when using -pedantic, __has_extension have the same behavior than __has_feature, so it is always be possible to disable extensions if needed.
> 
> Path to perform this change (if accepted) attached.

Thanks for doing this work.  I was previously ignorant of the difference between __has_feature and __has_extension.

I surveyed the differences and found only three where this change would actually impact libc++ (using tags/Apple/clang-211.9):

In C++03 mode the following features are turned on by using __has_extension but not by using __has_feature:

cxx_rvalue_references
cxx_reference_qualified_functions
cxx_deleted_functions

Does clang actually make these features work in C++03?  Or is the syntax merely accepted?

Howard