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Experiment using system::result operators #1164

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e45f290
more explicit result checking is removed
grisumbras May 25, 2026
bdcfc8f
even more explicit result checking is removed
grisumbras May 25, 2026
1fdf971
temp
grisumbras Jun 2, 2026
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128 changes: 55 additions & 73 deletions include/boost/json/detail/value_to.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -38,37 +38,34 @@ using reserve_implementation = mp11::mp_cond<
mp11::mp_true, mp11::mp_int<0>>;

template<class T>
error
try_reserve(
T&,
std::size_t size,
mp11::mp_int<2>)
system::result<T&>
try_reserve(T& cnt, std::size_t size, mp11::mp_int<2>)
noexcept
{
constexpr std::size_t N = std::tuple_size<remove_cvref<T>>::value;
if ( N != size )
return error::size_mismatch;
return error();
{
system::error_code ec;
BOOST_JSON_FAIL(ec, error::size_mismatch);
return {boost::system::in_place_error, ec};
}
return cnt;
}

template<typename T>
error
try_reserve(
T& cont,
std::size_t size,
mp11::mp_int<1>)
system::result<T&>
try_reserve(T& cnt, std::size_t size, mp11::mp_int<1>)
{
cont.reserve(size);
return error();
cnt.reserve(size);
return cnt;
}

template<typename T>
error
try_reserve(
T&,
std::size_t,
mp11::mp_int<0>)
system::result<T&>
try_reserve(T& cnt, std::size_t, mp11::mp_int<0>)
noexcept
{
return error();
return cnt;
}


Expand Down Expand Up @@ -212,35 +209,28 @@ value_to_impl(
value const& jv,
Ctx const& ctx )
{
object const* obj = jv.if_object();
if( !obj )
{
system::error_code ec;
BOOST_JSON_FAIL(ec, error::not_object);
return {boost::system::in_place_error, ec};
}

T res;
error const e = detail::try_reserve(
res, obj->size(), reserve_implementation<T>());
if( e != error() )
{
system::error_code ec;
BOOST_JSON_FAIL( ec, e );
return {boost::system::in_place_error, ec};
}

auto ins = detail::inserter(res, inserter_implementation<T>());
for( key_value_pair const& kv: *obj )
return jv.try_as_object() & [&](object const& jo)
{
auto elem_res = try_value_to<mapped_type<T>>( kv.value(), ctx );
if( elem_res.has_error() )
return {boost::system::in_place_error, elem_res.error()};
*ins++ = value_type<T>{
key_type<T>(kv.key()),
std::move(elem_res.unsafe_value())};
}
return res;
return detail::try_reserve(
res, jo.size(), reserve_implementation<T>())
& [&](T& res) -> system::result<T>
{
auto ins = detail::inserter(res, inserter_implementation<T>());
for(key_value_pair const& kv: jo)
{
auto elem_res = try_value_to<mapped_type<T>>(
kv.value(), ctx);
if( elem_res.has_error() )
return {
boost::system::in_place_error, elem_res.error()};
*ins++ = value_type<T>{
key_type<T>(kv.key()),
std::move( elem_res.unsafe_value() )};
}
return std::move(res);
};
};
}

// all other containers
Expand All @@ -252,33 +242,25 @@ value_to_impl(
value const& jv,
Ctx const& ctx )
{
array const* arr = jv.if_array();
if( !arr )
{
system::error_code ec;
BOOST_JSON_FAIL(ec, error::not_array);
return {boost::system::in_place_error, ec};
}

T result;
error const e = detail::try_reserve(
result, arr->size(), reserve_implementation<T>());
if( e != error() )
{
system::error_code ec;
BOOST_JSON_FAIL( ec, e );
return {boost::system::in_place_error, ec};
}

auto ins = detail::inserter(result, inserter_implementation<T>());
for( value const& val: *arr )
T res;
return jv.try_as_array() & [&](array const& ja)
{
auto elem_res = try_value_to<value_type<T>>( val, ctx );
if( elem_res.has_error() )
return {boost::system::in_place_error, elem_res.error()};
*ins++ = std::move(elem_res.unsafe_value());
}
return result;
return detail::try_reserve(
res, ja.size(), reserve_implementation<T>())
& [&](T& res) -> system::result<T>
{
auto ins = detail::inserter(res, inserter_implementation<T>());
for(value const& val: ja)
{
auto elem_res = try_value_to<value_type<T>>(val, ctx);
if( elem_res.has_error() )
return {
boost::system::in_place_error, elem_res.error()};
*ins++ = std::move( elem_res.unsafe_value() );
}
return std::move(res);
};
};
}

// tuple-like types
Expand Down
21 changes: 5 additions & 16 deletions include/boost/json/impl/value.ipp
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Original file line number Diff line number Diff line change
Expand Up @@ -528,37 +528,26 @@ value::try_as_null() const noexcept
boost::system::result<value&>
value::try_at(string_view key) noexcept
{
auto r = try_as_object();
if( !r )
return r.error();
return r.unsafe_value().try_at(key);
return try_as_object() & [key](object& jo) { return jo.try_at(key); };
}

boost::system::result<value const&>
value::try_at(string_view key) const noexcept
{
auto r = try_as_object();
if( !r )
return r.error();
return r.unsafe_value().try_at(key);
return try_as_object()
& [key](object const& jo) { return jo.try_at(key); };
}

boost::system::result<value&>
value::try_at(std::size_t pos) noexcept
{
auto r = try_as_array();
if( !r )
return r.error();
return r.unsafe_value().try_at(pos);
return try_as_array() & [pos](array& ja) { return ja.try_at(pos); };
}

boost::system::result<value const&>
value::try_at(std::size_t pos) const noexcept
{
auto r = try_as_array();
if( !r )
return r.error();
return r.unsafe_value().try_at(pos);
return try_as_array() & [pos](array const& ja) { return ja.try_at(pos); };
}

object const&
Expand Down
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