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Dear Qt, I love you but ...
... you are too slow and QJson API is so ugly.

Now using this wonderful json lib:
https://github.com/nlohmann/json

Results in release mode (QJson tests are not shown but
QJson was even slower than string concat).

PASS   : TestQgsJsonUtils::testExportAttributesJson(Use json)
RESULT : TestQgsJsonUtils::testExportAttributesJson():"Use json":
     0.0022 msecs per iteration (total: 75, iterations: 32768)
PASS   : TestQgsJsonUtils::testExportAttributesJson(Use old string concat)
RESULT : TestQgsJsonUtils::testExportAttributesJson():"Use old string concat":
     0.0032 msecs per iteration (total: 54, iterations: 16384)
PASS   : TestQgsJsonUtils::testExportFeatureJson(Use json)
RESULT : TestQgsJsonUtils::testExportFeatureJson():"Use json":
     0.011 msecs per iteration (total: 96, iterations: 8192)
PASS   : TestQgsJsonUtils::testExportFeatureJson(Use old string concat)
RESULT : TestQgsJsonUtils::testExportFeatureJson():"Use old string concat":
     0.015 msecs per iteration (total: 64, iterations: 4096)
PASS   : TestQgsJsonUtils::testExportGeomToJson(Use json)
RESULT : TestQgsJsonUtils::testExportGeomToJson():"Use json":
     0.76 msecs per iteration (total: 98, iterations: 128)
PASS   : TestQgsJsonUtils::testExportGeomToJson(Use old string concat)
RESULT : TestQgsJsonUtils::testExportGeomToJson():"Use old string concat":
     0.85 msecs per iteration (total: 55, iterations: 64)
PASS   : TestQgsJsonUtils::cleanupTestCase()
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elpaso committed Apr 18, 2019
1 parent 103981d commit 63711510b6831242fd3bb02b6b37204a1204b316
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#pragma once

#include <utility>

#include <nlohmann/detail/conversions/from_json.hpp>
#include <nlohmann/detail/conversions/to_json.hpp>

namespace nlohmann
{

template<typename, typename>
struct adl_serializer
{
/*!
@brief convert a JSON value to any value type
This function is usually called by the `get()` function of the
@ref basic_json class (either explicit or via conversion operators).
@param[in] j JSON value to read from
@param[in,out] val value to write to
*/
template<typename BasicJsonType, typename ValueType>
static auto from_json(BasicJsonType&& j, ValueType& val) noexcept(
noexcept(::nlohmann::from_json(std::forward<BasicJsonType>(j), val)))
-> decltype(::nlohmann::from_json(std::forward<BasicJsonType>(j), val), void())
{
::nlohmann::from_json(std::forward<BasicJsonType>(j), val);
}

/*!
@brief convert any value type to a JSON value
This function is usually called by the constructors of the @ref basic_json
class.
@param[in,out] j JSON value to write to
@param[in] val value to read from
*/
template <typename BasicJsonType, typename ValueType>
static auto to_json(BasicJsonType& j, ValueType&& val) noexcept(
noexcept(::nlohmann::to_json(j, std::forward<ValueType>(val))))
-> decltype(::nlohmann::to_json(j, std::forward<ValueType>(val)), void())
{
::nlohmann::to_json(j, std::forward<ValueType>(val));
}
};

} // namespace nlohmann

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