Fixed compilation error when index is not an int (issue #381)

CHANGELOG.md

@@ -5,6 +5,7 @@ HEAD
 ----
 
 * Added support for PROGMEM (issue #76)
+* Fixed compilation error when index is not an `int` (issue #381)
 
 v5.7.0
 ------

include/ArduinoJson/Internals/StringFuncs.hpp

@@ -44,6 +44,7 @@ struct CharPtrFuncs {
   }
 
   static const bool has_append = false;
+  static const bool has_equals = true;
   static const bool should_duplicate = false;
 };
 
@@ -56,6 +57,9 @@ struct StringFuncs<char*> : CharPtrFuncs {};
 template <size_t N>
 struct StringFuncs<char[N]> : CharPtrFuncs {};
 
+template <size_t N>
+struct StringFuncs<const char[N]> : CharPtrFuncs {};
+
 template <typename TString>
 struct StdStringFuncs {
   template <typename Buffer>
@@ -76,6 +80,7 @@ struct StdStringFuncs {
   }
 
   static const bool has_append = true;
+  static const bool has_equals = true;
   static const bool should_duplicate = true;
 };
 
@@ -108,6 +113,7 @@ struct StringFuncs<const __FlashStringHelper*> {
   }
 
   static const bool has_append = false;
+  static const bool has_equals = true;
   static const bool should_duplicate = true;
 };
 #endif

include/ArduinoJson/JsonObjectSubscript.hpp

@@ -84,13 +84,6 @@ template <typename TString>
 inline JsonObjectSubscript<TString> JsonObject::operator[](const TString& key) {
   return JsonObjectSubscript<TString>(*this, key);
 }
-
-template <typename TImplem>
-template <class TString>
-inline const JsonObjectSubscript<TString> JsonVariantBase<TImplem>::operator[](
-    const TString& key) const {
-  return asObject()[key];
-}
 }  // namespace ArduinoJson
 
 #ifdef _MSC_VER

include/ArduinoJson/JsonVariantBase.hpp

@@ -77,8 +77,12 @@ class JsonVariantBase : public Internals::JsonPrintable<TImpl> {
   // an object.
   // Return JsonVariant::invalid() if the variant is not an object.
   template <typename TString>
-  FORCE_INLINE const JsonObjectSubscript<TString> operator[](
-      const TString &key) const;
+  FORCE_INLINE
+      typename TypeTraits::EnableIf<Internals::StringFuncs<TString>::has_equals,
+                                    const JsonObjectSubscript<TString> >::type
+      operator[](const TString &key) const {
+    return asObject()[key];
+  }
 
  private:
   const TImpl *impl() const {

test/JsonVariant_Subscript_Tests.cpp

@@ -5,8 +5,8 @@
 // https://github.com/bblanchon/ArduinoJson
 // If you like this project, please add a star!
 
-#include <gtest/gtest.h>
 #include <ArduinoJson.h>
+#include <gtest/gtest.h>
 
 class JsonVariant_Subscript_Tests : public ::testing::Test {
  protected:
@@ -24,6 +24,9 @@ TEST_F(JsonVariant_Subscript_Tests, Array) {
   EXPECT_EQ(2, _variant.size());
   EXPECT_STREQ("element at index 0", _variant[0].asString());
   EXPECT_STREQ("element at index 1", _variant[1].asString());
+  EXPECT_STREQ(
+      "element at index 0",
+      _variant[static_cast<unsigned char>(0)].asString());  // issue #381
   EXPECT_FALSE(_variant[-1].success());
   EXPECT_FALSE(_variant[3].success());
   EXPECT_FALSE(_variant["0"].success());