On 11/10/2014 12:10 PM, Jason Merrill wrote:
On 11/10/2014 10:55 AM, Ed Smith-Rowland wrote:
Would a 4.9 version be accepted?
Sure.
What do you think about defining the macros for unsupported features
to 0 rather than leaving them undefined? The document doesn't seem to
specify.
Jason
Jason,
1. Undefined macros evaluate to 0 so that's effectively what we have now
- no change in behavior if we explicitly set them
2. The SD-6 document "advertises" direct use of macros with #if
__cpp_foobar without #ifdef - However if people are using #ifdef rather
than #if that might break things (I guess that's different behavior);
OTOH those dates are there for a reason.
3. OTOH, the SD-6 document seems to suggest only adding a macro as a
feature is implemented or allowed bycompiler flags - implying undefined
macros for unimplemented features
4. __has_include and __has_cpp_attribute return 0 on
non-existent/undefined so there's some precedent (though these are
rather different structurally - function macros)
So I'm conflicted after being initially sympathetic to defining as
zero. Still slightly in favor.
I'll might put this to the SD-6 list because it would be nice to have
clarity - even if it's "implementation defined".
Ed
