Added string deduplication (closes #1303)

src/ArduinoJson/Strings/ArduinoStringAdapter.hpp

@@ -39,6 +39,10 @@ class ArduinoStringAdapter {
     return _str->length();
   }
 
+  const char* begin() const {
+    return _str->c_str();
+  }
+
   typedef storage_policies::store_by_copy storage_policy;
 
  private:

src/ArduinoJson/Strings/ConstRamStringAdapter.hpp

@@ -39,6 +39,10 @@ class ConstRamStringAdapter {
     return _str;
   }
 
+  const char* begin() const {
+    return _str;
+  }
+
   typedef storage_policies::store_by_address storage_policy;
 
  protected:

src/ArduinoJson/Strings/FlashStringAdapter.hpp

@@ -5,6 +5,7 @@
 #pragma once
 
 #include <ArduinoJson/Polyfills/pgmspace.hpp>
+#include <ArduinoJson/Strings/FlashStringIterator.hpp>
 #include <ArduinoJson/Strings/IsString.hpp>
 #include <ArduinoJson/Strings/StoragePolicy.hpp>
 
@@ -42,6 +43,10 @@ class FlashStringAdapter {
     return strlen_P(reinterpret_cast<const char*>(_str));
   }
 
+  FlashStringIterator begin() const {
+    return FlashStringIterator(_str);
+  }
+
   typedef storage_policies::store_by_copy storage_policy;
 
  private:

src/ArduinoJson/Strings/FlashStringIterator.hpp

@@ -0,0 +1,44 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2020
+// MIT License
+
+#pragma once
+
+namespace ARDUINOJSON_NAMESPACE {
+
+class FlashStringIterator {
+ public:
+  explicit FlashStringIterator(const __FlashStringHelper* ptr)
+      : _ptr(reinterpret_cast<const char*>(ptr)) {}
+
+  explicit FlashStringIterator(const char* ptr) : _ptr(ptr) {}
+
+  FlashStringIterator operator+(ptrdiff_t d) const {
+    return FlashStringIterator(_ptr + d);
+  }
+
+  ptrdiff_t operator-(FlashStringIterator other) const {
+    return _ptr - other._ptr;
+  }
+
+  FlashStringIterator operator++(int) {
+    return FlashStringIterator(_ptr++);
+  }
+
+  FlashStringIterator operator++() {
+    return FlashStringIterator(++_ptr);
+  }
+
+  bool operator!=(FlashStringIterator other) const {
+    return _ptr != other._ptr;
+  }
+
+  char operator*() const {
+    return char(pgm_read_byte(_ptr));
+  }
+
+ private:
+  const char* _ptr;
+};
+
+}  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/Strings/SizedFlashStringAdapter.hpp

@@ -5,6 +5,7 @@
 #pragma once
 
 #include <ArduinoJson/Namespace.hpp>
+#include <ArduinoJson/Strings/FlashStringIterator.hpp>
 #include <ArduinoJson/Strings/IsString.hpp>
 #include <ArduinoJson/Strings/StoragePolicy.hpp>
 
@@ -41,6 +42,10 @@ class SizedFlashStringAdapter {
     return _size;
   }
 
+  FlashStringIterator begin() const {
+    return FlashStringIterator(_str);
+  }
+
   typedef storage_policies::store_by_copy storage_policy;
 
  private:

src/ArduinoJson/Strings/SizedRamStringAdapter.hpp

@@ -36,6 +36,10 @@ class SizedRamStringAdapter {
     return _size;
   }
 
+  const char* begin() const {
+    return _str;
+  }
+
   typedef storage_policies::store_by_copy storage_policy;
 
  private:

src/ArduinoJson/Strings/StlStringAdapter.hpp

@@ -41,6 +41,10 @@ class StlStringAdapter {
     return _str->size();
   }
 
+  const char* begin() const {
+    return _str->c_str();
+  }
+
   typedef storage_policies::store_by_copy storage_policy;
 
  private: