On Tuesday, 22 June 2021 21:52:16 CEST Jason Merrill wrote:
> > 2. About the namespace aliases: IIUC an attribute would currently be
> > rejected because of the C++ grammar. Do you want to make it valid before
> > WG21 officially decides how to proceed? And if you have a pointer for me
> > where I'd have to adjust the grammar rules, that'd help.
>
> You will want to adjust cp_parser_namespace_alias_definition to handle
> attributes like cp_parser_namespace_definition. The latter currently
> accepts attributes both before and after the name, which seems like a
> good pattern to follow so it doesn't matter which WG21 chooses.
> Probably best to pedwarn about C++11 attributes in both locations for
> now, not just after.
This introduces an ambiguity in cp_parser_declaration. The function has to
decide whether to call cp_parser_namespace_definition or fall back to
cp_parser_block_declaration (which calls
cp_parser_namespace_alias_definition). But now the parser has to look ahead a
lot farther:
namespace foo [[whatever]] {}
namespace bar [[whatever]] = foo;
I.e. only at '{' vs. '=' can cp_parser_declaration decide to call
cp_parser_namespace_definition.
Consequently, should I really modify cp_parser_namespace_definition to handle
namespace aliases? Or can/should cp_parser_declaration look ahead behind the
attribute(s)? How?
With pedantic standard C++ it would be easy, since only these attribute
placements are allowed:
namespace [[whatever] foo {}
namespace bar [[whatever]] = foo;
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Dr. Matthias Kretz https://mattkretz.github.io
GSI Helmholtz Centre for Heavy Ion Research https://gsi.de
std::experimental::simd https://github.com/VcDevel/std-simd
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