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Add string_view support

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This avoids unnecessary string copies on often used
find().
This commit is contained in:
Jamie Seward 2017-10-21 15:20:13 -07:00
parent 33df3250c3
commit 1a66679929
2 changed files with 40 additions and 9 deletions
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34
src/json.hpp
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@ -109,6 +109,16 @@ SOFTWARE.
#define JSON_UNLIKELY(x) x
#endif
// string_view support
#if defined(_MSC_VER) && defined(_HAS_CXX17)
#define JSON_USE_STRING_VIEW
#endif
#if defined(JSON_USE_STRING_VIEW)
#include <string_view>
#endif
/*!
@brief namespace for Niels Lohmann
@see https://github.com/nlohmann
@ -7589,12 +7599,28 @@ class basic_json
7159](http://rfc7159.net/rfc7159), because any order implements the
specified "unordered" nature of JSON objects.
*/
#if defined(JSON_USE_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;
#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;
#endif
/*!
@brief a type for an array
@ -10880,7 +10906,7 @@ class basic_json
@since version 1.0.0
*/
iterator find(typename object_t::key_type key)
iterator find(object_comparator_key_t key)
{
auto result = end();
@ -10894,9 +10920,9 @@ class basic_json
/*!
@brief find an element in a JSON object
@copydoc find(typename object_t::key_type)
@copydoc find(object_transparent_comparator_key_t)
*/
const_iterator find(typename object_t::key_type key) const
const_iterator find(object_comparator_key_t key) const
{
auto result = cend();
@ -10929,7 +10955,7 @@ class basic_json
@since version 1.0.0
*/
size_type count(typename object_t::key_type key) const
size_type count(object_comparator_key_t key) const
{
// return 0 for all nonobject types
return is_object() ? m_value.object->count(key) : 0;

5
test/CMakeLists.txt
View file

@ -80,6 +80,11 @@ if(MSVC)
# Disable warning C4566: character represented by universal-character-name '\uFF01' cannot be represented in the current code page (1252)
# Disable warning C4996: 'nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>::operator <<': was declared deprecated
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /wd4389 /wd4309 /wd4566 /wd4996")
if(MSVC_VERSION GREATER_EQUAL 1910)
# Enable c++17 support in Visual Studio 2017 (for testing string_view support)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /std:c++17")
endif()
endif()
#############################################################################