This rewrites our range adaptor implementation for more comprehensible
error messages, improved SFINAE behavior and conformance to P2281.
The diagnostic improvements mostly come from using appropriately named
functors instead of lambdas in the generic implementation of partial
application and composition of range adaptors, and in the definition of
each of the standard range adaptors. This makes their pretty printed
types much shorter and more self-descriptive.
The improved SFINAE behavior comes from constraining the range adaptors'
member functions appropriately. This improvement fixes PR99433, and is
also necessary in order to implement the wording changes of P2281.
Finally, P2281 clarified that partial application and composition of
range adaptors behaves like a perfect forwarding call wrapper. This
patch implements this, except that we don't bother adding overloads for
forwarding captured state entities as non-const lvalues, since it seems
sufficient to handle the const lvalue and non-const rvalue cases for now,
given the current set of standard range adaptors. But such overloads
can be easily added if they turn out to be needed.
libstdc++-v3/ChangeLog:
PR libstdc++/99433
* include/std/ranges (__adaptor::__maybe_refwrap): Remove.
(__adaptor::__adaptor_invocable): New concept.
(__adaptor::__adaptor_partial_app_viable): New concept.
(__adaptor::_RangeAdaptorClosure): Rewrite, turning it into a
non-template base class.
(__adaptor::_RangeAdaptor): Rewrite, turning it into a CRTP base
class template.
(__adaptor::_Partial): New class template that represents
partial application of a range adaptor non-closure.
(__adaptor::__pipe_invocable): New concept.
(__adaptor::_Pipe): New class template.
(__detail::__can_ref_view): New concept.
(__detail::__can_subrange): New concept.
(all): Replace the lambda here with ...
(_All): ... this functor. Add appropriate constraints.
(__detail::__can_filter_view): New concept.
(filter, _Filter): As in all/_All.
(__detail::__can_transform): New concept.
(transform, _Transform): As in all/_All.
(__detail::__can_take_view): New concept.
(take, _Take): As in all/_All.
(__detail::__can_take_while_view): New concept.
(take_while, _TakeWhile): As in all/_All.
(__detail::__can_drop_view): New concept.
(drop, _Drop): As in all/_All.
(__detail::__can_drop_while_view): New concept.
(drop_while, _DropWhile): As in all/_All.
(__detail::__can_join_view): New concept.
(join, _Join): As in all/_All.
(__detail::__can_split_view): New concept.
(split, _Split): As in all/_All. Rename template parameter
_Fp to _Pattern.
(__detail::__already_common): New concept.
(__detail::__can_common_view): New concept.
(common, _Common): As in all/_All.
(__detail::__can_reverse_view): New concept.
(reverse, _Reverse): As in all/_All.
(__detail::__can_elements_view): New concept.
(elements, _Elements): As in all/_All.
(keys, values): Adjust.
* testsuite/std/ranges/adaptors/99433.cc: New test.
* testsuite/std/ranges/adaptors/all.cc: No longer expect that
adding empty range adaptor closure objects to a pipeline doesn't
increase the size of the pipeline.
(test05): New test.
* testsuite/std/ranges/adaptors/common.cc (test03): New test.
* testsuite/std/ranges/adaptors/drop.cc (test09): New test.
* testsuite/std/ranges/adaptors/drop_while.cc (test04): New test.
* testsuite/std/ranges/adaptors/elements.cc (test04): New test.
* testsuite/std/ranges/adaptors/filter.cc (test06): New test.
* testsuite/std/ranges/adaptors/join.cc (test09): New test.
* testsuite/std/ranges/adaptors/p2281.cc: New test.
* testsuite/std/ranges/adaptors/reverse.cc (test07): New test.
* testsuite/std/ranges/adaptors/split.cc (test01, test04):
Adjust.
(test09): New test.
* testsuite/std/ranges/adaptors/split_neg.cc (test01): Adjust
expected error message.
(test02): Likewise. Extend test.
* testsuite/std/ranges/adaptors/take.cc (test06): New test.
* testsuite/std/ranges/adaptors/take_while.cc (test05): New test.
* testsuite/std/ranges/adaptors/transform.cc (test07, test08):
New test.
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