[PATCH] D27606: [libcxx] Fix tuple construction/assignment from types derived from tuple/pair/array.

[Eric Fiselier via Phabricator via cfe-commits]

EricWF created this revision.
EricWF added reviewers: mclow.lists, K-ballo, mpark.
EricWF added a subscriber: cfe-commits.

The standard requires tuple have the following constructors:

  tuple(tuple<OtherTypes...> const&);
  tuple(tuple<OtherTypes...> &&);
  tuple(pair<T1, T2> const&);
  tuple(pair<T1, T2> &&);
  tuple(array<T, N> const&);
  tuple(array<T, N> &&);

However libc++ implements these as a single constructor with the signature:

  template <class TupleLike, enable_if_t<__is_tuple_like<TupleLike>::value>>
  tuple(TupleLike&&);

This causes the constructor to reject types derived from tuple-like types; Unlike if we had all of the concrete overloads, because they cause the derived->base conversion in the signature.

This patch fixes this issue by detecting derived types and the tuple-like base they are derived from. It does this by creating an overloaded function with signatures for each of tuple/pair/array and checking if the possibly derived type can convert to any of them.

This patch fixes PR17550 <https://llvm.org/bugs/show_bug.cgi?id=17550>

This patch


https://reviews.llvm.org/D27606

Files:
  include/__tuple
  include/tuple
  include/type_traits
  test/std/utilities/tuple/tuple.tuple/tuple.assign/derived_from_tuple_like.pass.cpp
  test/std/utilities/tuple/tuple.tuple/tuple.cnstr/derived_from_tuple_like.pass.cpp
  test/support/propagate_value_category.hpp

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