From 33c6511dd0b04337ba4d0abe151ce826372ba551 Mon Sep 17 00:00:00 2001
From: Jamie Seward <jamie.d.seward@gmail.com>
Date: Mon, 23 Oct 2017 00:43:26 -0700
Subject: [PATCH] Remove JSON_HAS_STRING_VIEW
Instead implement @gregmarr's PR comments that perfect forwarding should be used. Also cleaned up cpp language standard detection.
---
src/json.hpp | 100 ++++++++++++++++++++++++++++++--------------
test/CMakeLists.txt | 2 +-
2 files changed, 70 insertions(+), 32 deletions(-)
diff --git a/src/json.hpp b/src/json.hpp
index 2e619c85..16b0b1fd 100644
--- a/src/json.hpp
+++ b/src/json.hpp
@@ -109,16 +109,14 @@ SOFTWARE.
#define JSON_UNLIKELY(x) x
#endif
-// string_view support
-#if (defined(__cplusplus) && __cplusplus >= 201703L) || (defined(_MSC_VER) && _MSC_VER > 1900 && defined(_HAS_CXX17) && _HAS_CXX17 == 1) // fix for issue #464
- #define JSON_HAS_STRING_VIEW
+// cpp language standard detection
+#if (defined(__cplusplus) && __cplusplus >= 201703L) || (defined(_HAS_CXX17) && _HAS_CXX17 == 1) // fix for issue #464
+ #define JSON_HAS_CPP_17
+ #define JSON_HAS_CPP_14
+#elif (defined(__cplusplus) && __cplusplus >= 201402L) || (defined(_HAS_CXX14) && _HAS_CXX14 == 1)
+ #define JSON_HAS_CPP_14
#endif
-#if defined(JSON_HAS_STRING_VIEW)
- #include <string_view>
-#endif
-
-
/*!
@brief namespace for Niels Lohmann
@see https://github.com/nlohmann
@@ -7600,26 +7598,18 @@ class basic_json
specified "unordered" nature of JSON objects.
*/
-#if defined(JSON_HAS_STRING_VIEW)
- // if std::string_view is to be used the object_t must
- // be declared with a transparent comparator
- // https://stackoverflow.com/questions/35525777/use-of-string-view-for-map-lookup
- using object_t = ObjectType<StringType,
- basic_json,
- std::less<>,
- AllocatorType<std::pair<const StringType,
- basic_json>>>;
-
- using object_comparator_key_t = std::string_view;
+#if defined(JSON_HAS_CPP_14)
+ // Use transparent comparator if possible, combined with perfect forwarding
+ // on find() and count() calls prevents unnecessary string construction.
+ using object_comparator_t = std::less<>;
#else
- using object_t = ObjectType<StringType,
- basic_json,
- std::less<StringType>,
- AllocatorType<std::pair<const StringType,
- basic_json>>>;
-
- using object_comparator_key_t = typename object_t::key_type;
+ using object_comparator_t = std::less<StringType>;
#endif
+ using object_t = ObjectType<StringType,
+ basic_json,
+ object_comparator_t,
+ AllocatorType<std::pair<const StringType,
+ basic_json>>>;
/*!
@brief a type for an array
@@ -9868,7 +9858,7 @@ class basic_json
#ifndef _MSC_VER // fix for issue #167 operator<< ambiguity under VS2015
and not std::is_same<ValueType, std::initializer_list<typename string_t::value_type>>::value
#endif
-#if defined(JSON_HAS_STRING_VIEW)
+#if defined(JSON_HAS_CPP_17)
and not std::is_same<ValueType, typename std::string_view>::value
#endif
, int >::type = 0 >
@@ -10906,7 +10896,7 @@ class basic_json
@since version 1.0.0
*/
- iterator find(object_comparator_key_t key)
+ iterator find(typename object_t::key_type key)
{
auto result = end();
@@ -10920,9 +10910,9 @@ class basic_json
/*!
@brief find an element in a JSON object
- @copydoc find(object_transparent_comparator_key_t)
+ @copydoc find(typename object_t::key_type)
*/
- const_iterator find(object_comparator_key_t key) const
+ const_iterator find(typename object_t::key_type key) const
{
auto result = cend();
@@ -10934,6 +10924,42 @@ class basic_json
return result;
}
+#ifdef JSON_HAS_CPP_14
+ /*!
+ @brief find an element in a JSON object
+ @copydoc find(typename object_t::key_type)
+ */
+ template<typename KeyT>
+ iterator find(KeyT&& key)
+ {
+ auto result = end();
+
+ if (is_object())
+ {
+ result.m_it.object_iterator = m_value.object->find(std::forward<KeyT>(key));
+ }
+
+ return result;
+ }
+
+ /*!
+ @brief find an element in a JSON object
+ @copydoc find(typename object_t::key_type)
+ */
+ template<typename KeyT>
+ const_iterator find(KeyT&& key) const
+ {
+ auto result = cend();
+
+ if (is_object())
+ {
+ result.m_it.object_iterator = m_value.object->find(std::forward<KeyT>(key));
+ }
+
+ return result;
+ }
+#endif
+
/*!
@brief returns the number of occurrences of a key in a JSON object
@@ -10955,12 +10981,24 @@ class basic_json
@since version 1.0.0
*/
- size_type count(object_comparator_key_t key) const
+ size_type count(typename object_t::key_type key) const
{
// return 0 for all nonobject types
return is_object() ? m_value.object->count(key) : 0;
}
+#ifdef JSON_HAS_CPP_14
+ /*!
+ @brief returns the number of occurrences of a key in a JSON object
+ @copydoc count(typename object_t::key_type)
+ */
+ template<typename KeyT>
+ size_type count(KeyT&& key) const
+ {
+ // return 0 for all nonobject types
+ return is_object() ? m_value.object->count(std::forward<KeyT>(key)) : 0;
+ }
+#endif
/// @}
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 1c1455a2..2c2c7479 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -82,7 +82,7 @@ if(MSVC)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /wd4389 /wd4309 /wd4566 /wd4996")
if(MSVC_VERSION GREATER_EQUAL 1910)
- # Enable c++17 support in Visual Studio 2017 (for testing string_view support)
+ # Enable c++17 support in Visual Studio 2017 (for testing perfect forwarding and transparent comparator in find() / count())
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /std:c++17")
endif()
endif()