[libcxx-commits] [PATCH] D114395: [libc++] Fix the return value of max_size()

[Arthur O'Dwyer via Phabricator via libcxx-commits]

Quuxplusone added inline comments.


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Comment at: libcxx/include/string_view:334
     _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
-    size_type max_size() const _NOEXCEPT { return numeric_limits<size_type>::max(); }
+    size_type max_size() const _NOEXCEPT { return (numeric_limits<size_type>::max() - sizeof(*this)) / sizeof(value_type); }
 
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(1) This seems unnecessarily fiddly; I don't really see anything wrong with the original.
(2) If we're going to do this, let's add a line break somewhere.
(3) Since `sv.size()` cannot physically return anything bigger than `PTRDIFF_MAX`, you probably want to use `ptrdiff_t` instead of `size_type` here... or maybe return `std::min(PTRDIFF_MAX, SIZE_MAX / sizeof(value_type))`? But again, this is needlessly fiddly and I see nothing wrong with just returning `SIZE_MAX` unconditionally. Literally nobody should ever be calling this method.

Do any of the other methods (e.g. the constructor) need to do something special to preserve the postcondition that `sv.size() <= sv.max_size()`? Before this change, the postcondition was vacuously true; now, it could conceivably be false, and maybe we need to check for that?


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D114395/new/

https://reviews.llvm.org/D114395