json/example/use_allocator.cpp at develop · boostorg/json · GitHub

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// Distributed under the Boost Software License, Version 1.0. (See accompanying

// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

// Official repository: https://github.com/boostorg/json

// tag::example_use_allocator[]

This example uses a context that stores an allocator to create sequences during conversions

#include <boost/container/pmr/monotonic_buffer_resource.hpp>

#include <boost/json.hpp>

#include <boost/system/errc.hpp>

#if defined(BOOST_CLANG) && BOOST_CLANG_VERSION > 40000

# pragma clang diagnostic push

# pragma clang diagnostic ignored "-Wunused-template"

#endif

#include <boost/container/pmr/vector.hpp>

#if defined(BOOST_CLANG) && BOOST_CLANG_VERSION > 40000

# pragma clang diagnostic pop

#endif

using namespace boost::json;

using namespace boost::container;

template< class Alloc >

struct use_allocator_t

{

Alloc allocator;

};

template< class Alloc >

use_allocator_t< Alloc >

use_allocator( Alloc alloc ) noexcept

{

return { alloc };

}

template<

class T,

class Alloc,

class FullContext,

class = typename std::enable_if<

is_sequence_like<T>::value &&

std::uses_allocator<T, Alloc>::value

>::type >

boost::system::result<T>

tag_invoke( try_value_to_tag<T>, const value& jv, const use_allocator_t<Alloc>& ctx, const FullContext& full_ctx )

{

array const* arr = jv.if_array();

if( !arr )

return {

boost::system::in_place_error,

make_error_code(boost::system::errc::invalid_argument) };

T result(ctx.allocator);

auto ins = std::inserter(result, result.end());

for( value const& val: *arr )

{

using ValueType = typename T::value_type;

auto elem_res = try_value_to<ValueType>( val, full_ctx );

if( elem_res.has_error() )

return {boost::system::in_place_error, elem_res.error()};

*ins++ = std::move(elem_res.unsafe_value());

}

return result;

}

int

main(int, char**)

{

value const jv = { 1, 2, 3, 4, 5, 6, 7, 8 };

unsigned char buf[1024];

pmr::monotonic_buffer_resource mr( buf, sizeof(buf) );

auto v = value_to< pmr::vector<int> >(

jv,

use_allocator( pmr::polymorphic_allocator<int>(&mr) ) );

assert( v.size() == jv.as_array().size() );

for( auto i = 0u; i < v.size(); ++i )

assert( v[i] == jv.at(i).to_number<int>() );

return EXIT_SUCCESS;

}

// end::example_use_allocator[]

json/example/use_allocator.cpp at develop · boostorg/json · GitHub

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