From f28157cab76a1150f62522185d7b0df49de5312f Mon Sep 17 00:00:00 2001
From: Benoit Blanchon <github@benoitblanchon.fr>
Date: Sun, 13 Nov 2016 20:19:36 +0100
Subject: [PATCH] Fixed compilation error when index is not an `int` (issue
 #381)

---
 CHANGELOG.md                                  | 1 +
 include/ArduinoJson/Internals/StringFuncs.hpp | 6 ++++++
 include/ArduinoJson/JsonObjectSubscript.hpp   | 7 -------
 include/ArduinoJson/JsonVariantBase.hpp       | 8 ++++++--
 test/JsonVariant_Subscript_Tests.cpp          | 5 ++++-
 5 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1689b4ff..f3a9193d 100644
--- a/CHANGELOG.md
+++ b/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
 ------
diff --git a/include/ArduinoJson/Internals/StringFuncs.hpp b/include/ArduinoJson/Internals/StringFuncs.hpp
index cb6b5cb1..91404d4d 100644
--- a/include/ArduinoJson/Internals/StringFuncs.hpp
+++ b/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
diff --git a/include/ArduinoJson/JsonObjectSubscript.hpp b/include/ArduinoJson/JsonObjectSubscript.hpp
index b56a2212..a5164b25 100644
--- a/include/ArduinoJson/JsonObjectSubscript.hpp
+++ b/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
diff --git a/include/ArduinoJson/JsonVariantBase.hpp b/include/ArduinoJson/JsonVariantBase.hpp
index 11c678d7..13875a94 100644
--- a/include/ArduinoJson/JsonVariantBase.hpp
+++ b/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 {
diff --git a/test/JsonVariant_Subscript_Tests.cpp b/test/JsonVariant_Subscript_Tests.cpp
index 069b95f9..c6b5c4fa 100644
--- a/test/JsonVariant_Subscript_Tests.cpp
+++ b/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());