Add ordering comparison operators

include/rcp.h

@@ -172,6 +172,38 @@ public:
         return static_cast<const void *>(ptr) != static_cast<const void *>(other.ptr);
     }
 
+    template <typename U>
+    bool operator<(const rcp<U> & other) const
+    {
+        return std::less<const void *>()(
+            static_cast<const void *>(ptr),
+            static_cast<const void *>(other.ptr));
+    }
+
+    template <typename U>
+    bool operator<=(const rcp<U> & other) const
+    {
+        return !std::less<const void *>()(
+            static_cast<const void *>(other.ptr),
+            static_cast<const void *>(ptr));
+    }
+
+    template <typename U>
+    bool operator>(const rcp<U> & other) const
+    {
+        return std::less<const void *>()(
+            static_cast<const void *>(other.ptr),
+            static_cast<const void *>(ptr));
+    }
+
+    template <typename U>
+    bool operator>=(const rcp<U> & other) const
+    {
+        return !std::less<const void *>()(
+            static_cast<const void *>(ptr),
+            static_cast<const void *>(other.ptr));
+    }
+
     bool operator==(std::nullptr_t) const
     {
         return ptr == nullptr;

tests.cpp

@@ -1,5 +1,6 @@
 #include <rcp.h>
 #include <cassert>
+#include <map>
 #include <unordered_map>
 #include <vector>
 
@@ -314,6 +315,25 @@ protected:
     ~Counter() { external_destruct++; }
 };
 
+void test_ordering()
+{
+    MyB a = MyB::create(1, 2);
+    MyB b = MyB::create(3, 4);
+    MyB a2 = a;
+    assert(!(a < a2));
+    assert(a <= a2);
+    assert(!(a > a2));
+    assert(a >= a2);
+    assert((a < b) != (b < a));
+    assert((a < b) == (b > a));
+    assert((a <= b) == (b >= a));
+    std::map<MyB, int> m;
+    m[a] = 1;
+    m[b] = 2;
+    assert(m[a2] == 1);
+    assert(m[b] == 2);
+}
+
 void test_use_count()
 {
     MyB a = MyB::create(1, 2);
@@ -382,6 +402,7 @@ int main(int argc, char * argv[])
     test_dynamic_cast_failure();
     test_dynamic_cast_move_success();
     test_dynamic_cast_move_failure();
+    test_ordering();
     test_use_count();
     test_swap();
     test_hash();