Added support for std::string_view (closes #1578, closes #1554)

src/ArduinoJson/Configuration.hpp

@@ -62,6 +62,17 @@
 #  endif
 #endif
 
+#ifndef ARDUINOJSON_ENABLE_STRING_VIEW
+#  ifdef __has_include
+#    if __has_include(<string_view>) && __cplusplus >= 201703L
+#      define ARDUINOJSON_ENABLE_STRING_VIEW 1
+#    endif
+#  endif
+#endif
+#ifndef ARDUINOJSON_ENABLE_STRING_VIEW
+#  define ARDUINOJSON_ENABLE_STRING_VIEW 0
+#endif
+
 #if ARDUINOJSON_EMBEDDED_MODE
 
 // Store floats by default to reduce the memory usage (issue #134)

src/ArduinoJson/Strings/StringAdapters.hpp

@@ -12,6 +12,10 @@
 #  include <ArduinoJson/Strings/StdStringAdapter.hpp>
 #endif
 
+#if ARDUINOJSON_ENABLE_STRING_VIEW
+#  include <ArduinoJson/Strings/StringViewAdapter.hpp>
+#endif
+
 #if ARDUINOJSON_ENABLE_ARDUINO_STRING
 #  include <ArduinoJson/Strings/ArduinoStringAdapter.hpp>
 #endif

src/ArduinoJson/Strings/StringViewAdapter.hpp

@@ -0,0 +1,56 @@
+// ArduinoJson - https://arduinojson.org
+// Copyright Benoit Blanchon 2014-2021
+// MIT License
+
+#pragma once
+
+#include <ArduinoJson/Namespace.hpp>
+#include <ArduinoJson/Strings/IsString.hpp>
+#include <ArduinoJson/Strings/StoragePolicy.hpp>
+
+#include <string_view>
+
+namespace ARDUINOJSON_NAMESPACE {
+
+class StringViewAdapter {
+ public:
+  StringViewAdapter(std::string_view str) : _str(str) {}
+
+  void copyTo(char* p, size_t n) const {
+    memcpy(p, _str.data(), n);
+  }
+
+  bool isNull() const {
+    return false;
+  }
+
+  int compare(const char* other) const {
+    if (!other)
+      return 1;
+    return _str.compare(other);
+  }
+
+  bool equals(const char* expected) const {
+    if (!expected)
+      return false;
+    return _str == expected;
+  }
+
+  size_t size() const {
+    return _str.size();
+  }
+
+  typedef storage_policies::store_by_copy storage_policy;
+
+ private:
+  std::string_view _str;
+};
+
+template <>
+struct IsString<std::string_view> : true_type {};
+
+inline StringViewAdapter adaptString(const std::string_view& str) {
+  return StringViewAdapter(str);
+}
+
+}  // namespace ARDUINOJSON_NAMESPACE