[gcc(refs/users/ppalka/heads/libstdcxx-ranges-algos-nieblification)] forward declare ranges::destroy

[Patrick Palka]

https://gcc.gnu.org/g:bc234336496de15491215ec6accedd066ad8a288

commit bc234336496de15491215ec6accedd066ad8a288
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Feb 13 12:31:10 2020 -0500

    forward declare ranges::destroy

Diff:
---
 libstdc++-v3/include/bits/ranges_uninitialized.h | 61 ++++++++++++++----------
 1 file changed, 36 insertions(+), 25 deletions(-)

diff --git a/libstdc++-v3/include/bits/ranges_uninitialized.h b/libstdc++-v3/include/bits/ranges_uninitialized.h
index a5b0c08..fa4238b 100644
--- a/libstdc++-v3/include/bits/ranges_uninitialized.h
+++ b/libstdc++-v3/include/bits/ranges_uninitialized.h
@@ -78,6 +78,22 @@ namespace ranges
 	   && __nothrow_forward_iterator<iterator_t<_Range>>);
   } // namespace __detail
 
+  struct __destroy_fn
+  {
+    template<__detail::__nothrow_input_iterator _Iter,
+	     __detail::__nothrow_sentinel<_Iter> _Sent>
+      requires destructible<iter_value_t<_Iter>>
+      constexpr _Iter
+      operator()(_Iter __first, _Sent __last) const noexcept;
+
+    template<__detail::__nothrow_input_range _Range>
+      requires destructible<range_value_t<_Range>>
+      constexpr safe_iterator_t<_Range>
+      operator()(_Range&& __r) const noexcept;
+  };
+
+  inline constexpr __destroy_fn destroy{};
+
   namespace __detail
   {
     template<typename _Iter>
@@ -505,32 +521,27 @@ namespace ranges
 
   inline constexpr __destroy_at_fn destroy_at{};
 
-  struct __destroy_fn
-  {
-    template<__detail::__nothrow_input_iterator _Iter,
-	     __detail::__nothrow_sentinel<_Iter> _Sent>
-      requires destructible<iter_value_t<_Iter>>
-      constexpr _Iter
-      operator()(_Iter __first, _Sent __last) const noexcept
-      {
-	if constexpr (is_trivially_destructible_v<iter_value_t<_Iter>>)
-	  return ranges::next(__first, __last);
-	else
-	  {
-	    for (; __first != __last; ++__first)
-	      ranges::destroy_at(std::__addressof(*__first));
-	    return __first;
-	  }
-      }
-
-    template<__detail::__nothrow_input_range _Range>
-      requires destructible<range_value_t<_Range>>
-      constexpr safe_iterator_t<_Range>
-      operator()(_Range&& __r) const noexcept
-      { return (*this)(ranges::begin(__r), ranges::end(__r)); }
-  };
+  template<__detail::__nothrow_input_iterator _Iter,
+	   __detail::__nothrow_sentinel<_Iter> _Sent>
+    requires destructible<iter_value_t<_Iter>>
+    constexpr _Iter
+    __destroy_fn::operator()(_Iter __first, _Sent __last) const noexcept
+    {
+      if constexpr (is_trivially_destructible_v<iter_value_t<_Iter>>)
+	return ranges::next(__first, __last);
+      else
+	{
+	  for (; __first != __last; ++__first)
+	    ranges::destroy_at(std::__addressof(*__first));
+	  return __first;
+	}
+    }
 
-  inline constexpr __destroy_fn destroy{};
+  template<__detail::__nothrow_input_range _Range>
+    requires destructible<range_value_t<_Range>>
+    constexpr safe_iterator_t<_Range>
+    __destroy_fn::operator()(_Range&& __r) const noexcept
+    { return (*this)(ranges::begin(__r), ranges::end(__r)); }
 
   struct __destroy_n_fn
   {