Add a convenience function to test if a property has a binding

Closes #74.

src/kdbindings/property.h

@@ -108,8 +108,8 @@ struct equal_to {
 // Property can declare PropertyNode as a friend
 // class.
 namespace Private {
-    template<typename PropertyType>
-    class PropertyNode;
+template<typename PropertyType>
+class PropertyNode;
 }
 
 /**
@@ -300,6 +300,11 @@ class Property
      */
     Signal<> &destroyed() const { return m_destroyed; }
 
+    /**
+     * Returns true if this Property has a binding associated with it.
+     */
+    bool hasBinding() const noexcept { return m_updater.get() != nullptr; }
+
     /**
      * Assign a new value to this Property.
      *

tests/property/tst_property.cpp

@@ -261,6 +261,15 @@ TEST_CASE("Property Updators")
         REQUIRE(slotCalled);
         REQUIRE(updatedValue == 123);
     }
+
+    SUBCASE("Can query a property to see if it has an updater")
+    {
+        Property<int> property(std::make_unique<DummyPropertyUpdater>(7));
+        REQUIRE(property.hasBinding() == true);
+
+        Property<int> property2(7);
+        REQUIRE(property2.hasBinding() == false);
+    }
 }
 
 TEST_CASE("Moving")