LWG3715 view_interface::empty is overconstrained

Author: burblebee

source/ranges.tex

@@ -1537,11 +1537,17 @@
     }
 
   public:
-    constexpr bool empty() requires @\libconcept{forward_range}@<D> {
-      return ranges::begin(@\exposid{derived}@()) == ranges::end(@\exposid{derived}@());
+    constexpr bool empty() requires @\libconcept{sized_range}@<D> || @\libconcept{forward_range}@<D> {
+      if constexpr (@\libconcept{sized_range}@<D>)
+        return ranges::size(@\exposid{derived}@()) == 0;
+      else
+        return ranges::begin(@\exposid{derived}@()) == ranges::end(@\exposid{derived}@());
     }
-    constexpr bool empty() const requires @\libconcept{forward_range}@<const D> {
-      return ranges::begin(@\exposid{derived}@()) == ranges::end(@\exposid{derived}@());
+    constexpr bool empty() const requires @\libconcept{sized_range}@<const D> || @\libconcept{forward_range}@<const D> {
+      if constexpr (@\libconcept{sized_range}@<const D>)
+        return ranges::size(@\exposid{derived}@()) == 0;
+      else
+        return ranges::begin(@\exposid{derived}@()) == ranges::end(@\exposid{derived}@());
     }
 
     constexpr explicit operator bool()