Add tag::as method

2 files changed, 26 insertions, 5 deletions

diff --git a/include/tag.h b/include/tag.h
index 58b99c082c..569da446d6 100644
--- a/include/tag.h
+++ b/include/tag.h
@@ -71,6 +71,15 @@ public:
     std::unique_ptr<tag> clone() &&;
 
     /**
+     * @brief Returns a reference to the tag as an instance of T
+     * @throw std::bad_cast if the tag is not of type T
+     */
+    template<class T>
+    T& as();
+    template<class T>
+    const T& as() const;
+
+    /**
      * @brief Move-assigns the given tag if the class is the same
      * @throw std::bad_cast if @c rhs is not the same type as @c *this
      */
@@ -101,6 +110,20 @@ private:
 
 std::ostream& operator<<(std::ostream& os, tag_type tt);
 
+template<class T>
+T& tag::as()
+{
+    static_assert(std::is_base_of<tag, T>::value, "T must be a subclass of tag");
+    return dynamic_cast<T&>(*this);
+}
+
+template<class T>
+const T& tag::as() const
+{
+    static_assert(std::is_base_of<tag, T>::value, "T must be a subclass of tag");
+    return dynamic_cast<const T&>(*this);
+}
+
 }
 
 #endif // TAG_H_INCLUDED
diff --git a/include/value.h b/include/value.h
index c017bcbd27..4865c8fd1c 100644
--- a/include/value.h
+++ b/include/value.h
@@ -93,7 +93,7 @@ public:
     const tag& get() const;
 
     /**
-     * @brief Returns the contained tag as an instance of T
+     * @brief Returns a reference to the contained tag as an instance of T
      * @throw std::bad_cast if the tag is not of type T
      */
     template<class T>
@@ -207,15 +207,13 @@ private:
 template<class T>
 T& value::as()
 {
-    static_assert(std::is_base_of<tag, T>::value, "T must be a subclass of tag");
-    return dynamic_cast<T&>(get());
+    return tag_->as<T>();
 }
 
 template<class T>
 const T& value::as() const
 {
-    static_assert(std::is_base_of<tag, T>::value, "T must be a subclass of tag");
-    return dynamic_cast<T&>(get());
+    return tag_->as<T>();;
 }
 
 }