P0074R0 Making std::owner_less more flexible

Author: Dawn Perchik

source/utilities.tex

@@ -6679,7 +6679,7 @@
 
 \begin{codeblock}
 namespace std {
-  template<class T> struct owner_less;
+  template<class T = void> struct owner_less;
 
   template<class T> struct owner_less<shared_ptr<T> > {
     typedef bool result_type;
@@ -6698,6 +6698,19 @@
     bool operator()(shared_ptr<T> const&, weak_ptr<T> const&) const;
     bool operator()(weak_ptr<T> const&, shared_ptr<T> const&) const;
   };
+
+  template<> struct owner_less<void> {
+    template<class T, class U>
+      bool operator()(shared_ptr<T> const&, shared_ptr<U> const&) const;
+    template<class T, class U>
+      bool operator()(shared_ptr<T> const&, weak_ptr<U> const&) const;
+    template<class T, class U>
+      bool operator()(weak_ptr<T> const&, shared_ptr<U> const&) const;
+    template<class T, class U>
+      bool operator()(weak_ptr<T> const&, weak_ptr<U> const&) const;
+
+    typedef unspecified is_transparent;
+  };
 }
 \end{codeblock}