mclow.lists added inline comments.
================
Comment at: include/string_view:216
@@ +215,3 @@
+ basic_string_view(const _CharT* __s)
+ : __data(__s), __size(_Traits::length(__s)) {}
+
----------------
kimgr wrote:
> mclow.lists wrote:
> > kimgr wrote:
> > > I'm working from the paper at https://isocpp.org/files/papers/N3762.html,
> > > and I find it a little sketchy on the policy for nullptrs.
> > >
> > > Since the ctor above accepts nullptr as long as the length is zero, would
> > > it make sense to do that here too? That is, only call _Traits::length for
> > > non-nullptr __s args?
> > Reading from N4600: Requires: `[str, str + traits::length(str))` is a valid
> > range.
> >
> > So, no - passing `nullptr` here is undefined.
> >
> OK, that feels more principled to me, anyway.
>
> But the `(const char*, size_t)` constructor has the same requirement and it
> *does* accept `nullptr`, provided the length is zero. I saw you had to get
> rid of the assertion, but I feel like the constructor should probably not
> silently accept `nullptr` for zero-sized strings. Or do you know if that's
> intentional? Many StringRef/StringPiece implementations seem to have the same
> behavior.
It is absolutely intentional. `[nullptr, nullptr+0)` is a perfectly fine
half-open range. It contains no characters.
However, the ctor that takes just a pointer has to calculate the length .. by
dereferencing the pointer.
I had to get rid of the assertion because one of the bots (gcc 4.9) has a bug
about constexpr ctors in c++11 mode. Even though the assertion was `#ifdef`ed
on C++ > 11, the compiler complained about it. I'll be putting the assertion
back as soon as I can figure out how to keep gcc from complaining.
https://reviews.llvm.org/D21459
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