Replace node's YAML_CPP_OPERATOR_BOOL macro with an explicit bool operator (#755)

include/yaml-cpp/node/detail/bool_type.h

-#ifndef NODE_DETAIL_BOOL_TYPE_H_62B23520_7C8E_11DE_8A39_0800200C9A66
-#define NODE_DETAIL_BOOL_TYPE_H_62B23520_7C8E_11DE_8A39_0800200C9A66
-
-#if defined(_MSC_VER) ||                                            \
-    (defined(__GNUC__) && (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || \
-     (__GNUC__ >= 4))  // GCC supports "pragma once" correctly since 3.4
-#pragma once
-#endif
-
-namespace YAML {
-namespace detail {
-struct unspecified_bool {
-  struct NOT_ALLOWED;
-  static void true_value(NOT_ALLOWED*) {}
-};
-using unspecified_bool_type = void (*)(unspecified_bool::NOT_ALLOWED *);
-}
-}
-
-#define YAML_CPP_OPERATOR_BOOL()                                            \
-  operator YAML::detail::unspecified_bool_type() const {                    \
-    return this->operator!() ? 0                                            \
-                             : &YAML::detail::unspecified_bool::true_value; \
-  }
-
-#endif  // NODE_DETAIL_BOOL_TYPE_H_62B23520_7C8E_11DE_8A39_0800200C9A66

include/yaml-cpp/node/node.h

@@ -13,7 +13,6 @@
 #include "yaml-cpp/dll.h"
 #include "yaml-cpp/emitterstyle.h"
 #include "yaml-cpp/mark.h"
-#include "yaml-cpp/node/detail/bool_type.h"
 #include "yaml-cpp/node/detail/iterator_fwd.h"
 #include "yaml-cpp/node/ptr.h"
 #include "yaml-cpp/node/type.h"
@@ -59,7 +58,7 @@ class YAML_CPP_API Node {
   bool IsMap() const { return Type() == NodeType::Map; }
 
   // bool conversions
-  YAML_CPP_OPERATOR_BOOL()
+  explicit operator bool() const { return IsDefined(); }
   bool operator!() const { return !IsDefined(); }
 
   // access