[PATCH] D112981: Fix iterator_adaptor_base/enumerator_iter to allow composition of llvm::enumerate with llvm::make_filter_range

[River Riddle via Phabricator via llvm-commits]

rriddle added a comment.

In D112981#3101944 <https://reviews.llvm.org/D112981#3101944>, @mehdi_amini wrote:

>> Can you update the description with information on what this is fixing?
>
> I am not sure how to phrase this, the first error was:
>
>   /llvm/include/llvm/ADT/iterator.h:299:41: error: binding reference of type 'result_pair<...>' to value of type 'const result_pair<...>' drops 'const' qualifier
>     ReferenceT operator*() const { return *I; }
>                                           ^~
>   llvm/unittests/ADT/IteratorTest.cpp:186:26: note: in instantiation of member function 'llvm::iterator_adaptor_base<llvm::filter_iterator_base<llvm::detail::enumerator_iter<int (&)[7]>, (lambda at llvm/unittests/ADT/IteratorTest.cpp:182:16), std::forward_iterator_tag>, llvm::detail::enumerator_iter<int (&)[7]>, std::forward_iterator_tag, llvm::detail::result_pair<int (&)[7]>, long, int *, llvm::detail::result_pair<int (&)[7]> &>::operator*' requested here
>     for (auto IndexedValue : make_filter_range(Enumerate, IsOdd))
>                            ^
>
> The fix in STLExtra is for:
>
>   llvm/unittests/ADT/IteratorTest.cpp:187:34: error: member reference base type 'int' is not a structure or union
>       Actual.push_back(IndexedValue.value());
>                        ~~~~~~~~~~~~^~~~~~
>   In file included from llvm/unittests/ADT/IteratorTest.cpp:10:
>   llvm/include/llvm/ADT/iterator.h:300:35: error: non-const lvalue reference to type 'int' cannot bind to a value of unrelated type 'llvm::detail::enumerator_iter<int (&)[7]>::result_type' (aka 'result_pair<int (&)[7]>')
>     ReferenceT operator*() { return *I; }
>                                     ^~
>   llvm/unittests/ADT/IteratorTest.cpp:186:26: note: in instantiation of member function 'llvm::iterator_adaptor_base<llvm::filter_iterator_base<llvm::detail::enumerator_iter<int (&)[7]>, (lambda at llvm/unittests/ADT/IteratorTest.cpp:182:16), std::forward_iterator_tag>, llvm::detail::enumerator_iter<int (&)[7]>, std::forward_iterator_tag, llvm::detail::result_pair<int (&)[7]>, long, int *, int &>::operator*' requested here
>     for (auto IndexedValue : make_filter_range(Enumerate, IsOdd))
>                            ^

It was more of a passing comment, but something as simple as:

  * Properly specify reference type in enumerator_iter
  * Fix constness of iterator_adaptor_base::operator*


Repository:
  rG LLVM Github Monorepo

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https://reviews.llvm.org/D112981