[PATCH 3/3] libstdc++: Implement C++20 range adaptors

[Jonathan Wakely]

On 18/02/20 21:11 +0100, Stephan Bergmann wrote:
>On 18/02/2020 12:56, Jonathan Wakely wrote:
>>Does this solve the problem, and work with both compilers?
>>
>>diff --git a/libstdc++-v3/include/std/ranges 
>>b/libstdc++-v3/include/std/ranges
>>index b9ac528fdff..481ba75ee5e 100644
>>--- a/libstdc++-v3/include/std/ranges
>>+++ b/libstdc++-v3/include/std/ranges
>>@@ -1102,6 +1102,9 @@ namespace views
>>           }
>>        };
>>
>>+    template<typename _Callable>
>>+      _RangeAdaptor(_Callable) -> _RangeAdaptor<_Callable>;
>>+
>>      template<typename _Callable>
>>        struct _RangeAdaptorClosure : public _RangeAdaptor<_Callable>
>>        {
>>
>>
>>With this deduction guide CTAD should work, without having to consider
>>the constraints on the constructors.
>
>Yes, that indeed compiles with both GCC and Clang.

Fixed with this patch, which also introduces some new typedefs to
avoid having to evaluate the iterator_t alias template again and
again.

Tested powerpc64le-linux, committed to master.

There's still something not quite right, because this compiles fine
with GCC but not with Clang:

#include <ranges>
int main()
{
   int a[1] = { 2 };
   auto f = a | std::views::filter([](auto&&){return true;});
   return *std::ranges::begin(f);
}

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