Added JsonVariant::operator| to return a default value

src/ArduinoJson/JsonVariantBase.hpp

@@ -6,6 +6,7 @@
 
 #include "JsonVariantCasts.hpp"
 #include "JsonVariantComparisons.hpp"
+#include "JsonVariantOr.hpp"
 #include "JsonVariantSubscripts.hpp"
 #include "Serialization/JsonPrintable.hpp"
 
@@ -15,6 +16,7 @@ template <typename TImpl>
 class JsonVariantBase : public Internals::JsonPrintable<TImpl>,
                         public JsonVariantCasts<TImpl>,
                         public JsonVariantComparisons<TImpl>,
+                        public JsonVariantOr<TImpl>,
                         public JsonVariantSubscripts<TImpl>,
                         public TypeTraits::JsonVariantTag {};
 }

src/ArduinoJson/JsonVariantOr.hpp

@@ -0,0 +1,36 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2017
+// MIT License
+
+#pragma once
+
+#include "Data/JsonVariantAs.hpp"
+#include "Polyfills/attributes.hpp"
+
+namespace ArduinoJson {
+
+template <typename TImpl>
+class JsonVariantOr {
+ public:
+  // Returns the default value if the JsonVariant is undefined of incompatible
+  template <typename T>
+  T operator|(const T &defaultValue) const {
+    if (impl()->template is<T>())
+      return impl()->template as<T>();
+    else
+      return defaultValue;
+  }
+
+  // Returns the default value if the JsonVariant is undefined of incompatible
+  // Special case for string: null is treated as undefined
+  const char *operator|(const char *defaultValue) const {
+    const char *value = impl()->template as<const char *>();
+    return value ? value : defaultValue;
+  }
+
+ private:
+  const TImpl *impl() const {
+    return static_cast<const TImpl *>(this);
+  }
+};
+}