aaron.ballman added inline comments.
================
Comment at: libcxx/include/regex:2520
+ _LIBCPP_PREFERRED_NAME(wregex)
+ basic_regex
{
----------------
rsmith wrote:
> Quuxplusone wrote:
> > Why does this attribute go on the class template? Shouldn't it be an
> > attribute on the typedef, so that you don't have to repeat yourself? I
> > mean, I'd much rather see
> >
> > template<class T> class BasicFoo { };
> > using [[preferred]] Foo = BasicFoo<A>;
> > using [[preferred]] WFoo = BasicFoo<B>;
> >
> > than
> >
> > template<class> class BasicFoo;
> > using Foo = BasicFoo<A>;
> > using WFoo = BasicFoo<B>;
> > template<class T> class [[preferred(Foo, WFoo)]] BasicFoo { };
> >
> > The latter repeats every identifier one extra time, compared to the former.
> >
> > And then, in fact, couldn't you go one step further and say that typedefs
> > in the same scope as the class template itself should //always// implicitly
> > have this attribute? Even if the attribute doesn't appear in the source
> > code, we still want to print `basic_regex<char>` as `regex`, right? It
> > shouldn't cost any additional work for the compiler to figure that out.
> I don't think we want arbitrary typedefs to be able to declare themselves to
> be names for the class template after the fact: this is a decision that the
> (author of the) template itself should be making, not a decision for the
> (author of the) typedef. Also, we need the information when looking at the
> class template, not when looking at the typedef, so attaching it to the
> typedef would require us to internally attach it to the class template
> instead anyway, and generally it's undesirable and problematic to mutate an
> existing declaration -- it's much cleaner to introduce new properties of a
> declaration by redeclaring it. It's certainly not ideal that this results in
> extra forward declarations in some cases, but given that this attribute is
> only expected to be written a few dozen times in total, it doesn't seem worth
> worrying about too much.
>
> I don't think we want typedefs to automatically get this behavior, even if
> they're in the same namespace. I think it would be problematic if, for
> example:
>
> ```
> namespace absl {
> template<typename T> struct basic_string_view;
> using format_arg = basic_string_view<char>;
> std::string format(format_arg, ...);
> }
> ```
>
> ... resulted in `absl::string_view` sometimes displaying as the (to a user)
> unrelated type `absl::format_arg` depending on (presumably) `#include` order,
> and I don't think we want to be in the business of inventing heuristics to
> pick the "right" typedef.
> I don't think we want arbitrary typedefs to be able to declare themselves to
> be names for the class template after the fact: this is a decision that the
> (author of the) template itself should be making, not a decision for the
> (author of the) typedef.
+1
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D91311/new/
https://reviews.llvm.org/D91311
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