Add value::as method for conversion

Make conversion operators explicit

2 files changed, 32 insertions, 8 deletions

diff --git a/include/value.h b/include/value.h
index a03395c2d1..c82aeb9097 100644
--- a/include/value.h
+++ b/include/value.h
@@ -66,6 +66,15 @@ public:
     tag& get();
     const tag& get() const;
 
+    /**
+     * @brief Returns the contained 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;
+
     //Assignment of primitives and string
     /**
      * @brief Assigns the given value to the tag if the type is compatible
@@ -92,12 +101,12 @@ public:
      * @throw std::bad_cast if the tag type is not convertible to the desired
      * type via a widening conversion
      */
-    operator int8_t() const;
-    operator int16_t() const;
-    operator int32_t() const;
-    operator int64_t() const;
-    operator float() const;
-    operator double() const;
+    explicit operator int8_t() const;
+    explicit operator int16_t() const;
+    explicit operator int32_t() const;
+    explicit operator int64_t() const;
+    explicit operator float() const;
+    explicit operator double() const;
 
     /**
      * @brief Returns the contained string if the type is tag_string
@@ -105,7 +114,7 @@ public:
      * If the value is uninitialized, the behavior is undefined.
      * @throw std::bad_cast if the tag type is not tag_string
      */
-    operator const std::string&() const;
+    explicit operator const std::string&() const;
 
     ///Returns true if the value is not uninitialized
     explicit operator bool() const;
@@ -167,6 +176,18 @@ private:
     std::unique_ptr<tag> tag_;
 };
 
+template<class T>
+T& value::as()
+{
+    return dynamic_cast<T&>(get());
+}
+
+template<class T>
+const T& value::as() const
+{
+    return dynamic_cast<T&>(get());
+}
+
 }
 
 #endif // TAG_REF_PROXY_H_INCLUDED
diff --git a/test/nbttest.cpp b/test/nbttest.cpp
index 89ecdf8f85..ac9e5d5a30 100644
--- a/test/nbttest.cpp
+++ b/test/nbttest.cpp
@@ -199,6 +199,9 @@ void test_value()
     valstr = "bar";
     EXPECT_EXCEPTION(valstr = 5, std::bad_cast);
     ASSERT(std::string(valstr) == "bar");
+    ASSERT(valstr.as<tag_string>() == "bar");
+    ASSERT(&valstr.as<tag>() == &valstr.get());
+    EXPECT_EXCEPTION(valstr.as<tag_float>(), std::bad_cast);
 
     val1 = int64_t(42);
     ASSERT(val2 != val1);
@@ -227,7 +230,7 @@ void test_value()
     tag = 21;
     ASSERT(int32_t(val3) == 21);
     val1.set_ptr(std::move(val3.get_ptr()));
-    ASSERT(tag_int(val1) == 21);
+    ASSERT(val1.as<tag_int>() == 21);
 
     ASSERT(val1.get_type() == tag_type::Int);
     ASSERT(val2.get_type() == tag_type::Null);