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

Author: bblanchon

CHANGELOG.md

@@ -9,6 +9,7 @@ HEAD
 * Fixed `serializeJson(doc, String)` when allocation fails (issue #1572)
 * Fixed clang-tidy warnings (issue #1574, PR #1577 by @armandas)
 * Added fake class `InvalidConversion<T1,T2>` to easily identify invalid conversions (issue #1585)
+* Added support for `std::string_view` (issue #1578, PR #1554 by @0xFEEDC0DE64)
 
 v6.18.0 (2021-05-05)
 -------

extras/tests/CMakeLists.txt

@@ -11,6 +11,7 @@ link_libraries(ArduinoJson catch)
 
 include_directories(Helpers)
 add_subdirectory(Cpp11)
+add_subdirectory(Cpp17)
 add_subdirectory(FailingBuilds)
 add_subdirectory(IntegrationTests)
 add_subdirectory(JsonArray)

extras/tests/Cpp17/CMakeLists.txt

@@ -0,0 +1,29 @@
+# ArduinoJson - https://arduinojson.org
+# Copyright Benoit Blanchon 2014-2021
+# MIT License
+
+if(MSVC_VERSION LESS 1910)
+	return()
+endif()
+
+if(CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5)
+	return()
+endif()
+
+if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 7)
+	return()
+endif()
+
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
+add_executable(Cpp17Tests
+	string_view.cpp
+)
+
+add_test(Cpp17 Cpp17Tests)
+
+set_tests_properties(Cpp17
+	PROPERTIES
+		LABELS 		"Catch"
+)

extras/tests/Cpp17/string_view.cpp

@@ -0,0 +1,79 @@
+#include <ArduinoJson.h>
+
+#include <catch.hpp>
+#include <string_view>
+
+#if !ARDUINOJSON_ENABLE_STRING_VIEW
+#  error ARDUINOJSON_ENABLE_STRING_VIEW must be set to 1
+#endif
+
+TEST_CASE("string_view") {
+  StaticJsonDocument<128> doc;
+  JsonVariant variant = doc.to<JsonVariant>();
+
+  SECTION("deserializeJson()") {
+    auto err = deserializeJson(doc, std::string_view("123", 2));
+    REQUIRE(err == DeserializationError::Ok);
+    REQUIRE(doc.as<int>() == 12);
+  }
+
+  SECTION("JsonDocument::set()") {
+    doc.set(std::string_view("123", 2));
+    REQUIRE(doc.as<std::string>() == "12");
+  }
+
+  SECTION("JsonDocument::operator[]() const") {
+    doc["ab"] = "Yes";
+    doc["abc"] = "No";
+    REQUIRE(doc[std::string_view("abc", 2)] == "Yes");
+  }
+
+  SECTION("JsonDocument::operator[]()") {
+    doc[std::string_view("abc", 2)] = "Yes";
+    REQUIRE(doc["ab"] == "Yes");
+  }
+
+  SECTION("JsonVariant::operator==()") {
+    variant.set("A");
+    REQUIRE(variant == std::string_view("AX", 1));
+    REQUIRE_FALSE(variant == std::string_view("BX", 1));
+  }
+
+  SECTION("JsonVariant::operator>()") {
+    variant.set("B");
+    REQUIRE(variant > std::string_view("AX", 1));
+    REQUIRE_FALSE(variant > std::string_view("CX", 1));
+  }
+
+  SECTION("JsonVariant::operator<()") {
+    variant.set("B");
+    REQUIRE(variant < std::string_view("CX", 1));
+    REQUIRE_FALSE(variant < std::string_view("AX", 1));
+  }
+
+  SECTION("String deduplication") {
+    doc.add(std::string_view("example one", 7));
+    REQUIRE(doc.memoryUsage() == JSON_ARRAY_SIZE(1) + 8);
+
+    doc.add(std::string_view("example two", 7));
+    REQUIRE(doc.memoryUsage() == JSON_ARRAY_SIZE(2) + 8);
+  }
+}
+
+using ARDUINOJSON_NAMESPACE::adaptString;
+
+TEST_CASE("StringViewAdapter") {
+  std::string_view str("bravoXXX", 5);
+  auto adapter = adaptString(str);
+
+  CHECK(adapter.compare(NULL) > 0);
+  CHECK(adapter.compare("alpha") > 0);
+  CHECK(adapter.compare("bravo") == 0);
+  CHECK(adapter.compare("charlie") < 0);
+
+  CHECK(adapter.equals("bravo"));
+  CHECK_FALSE(adapter.equals("charlie"));
+  CHECK_FALSE(adapter.equals(NULL));
+
+  CHECK(adapter.size() == 5);
+}

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