328 lines
10 KiB
C++
328 lines
10 KiB
C++
//
|
|
// Copyright (c) 2019 Vinnie Falco (vinnie.falco@gmail.com)
|
|
// Copyright (c) 2020 Krystian Stasiowski (sdkrystian@gmail.com)
|
|
// Copyright (c) 2022 Dmitry Arkhipov (grisumbras@gmail.com)
|
|
//
|
|
// 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
|
|
//
|
|
|
|
#ifndef BOOST_JSON_VALUE_TO_HPP
|
|
#define BOOST_JSON_VALUE_TO_HPP
|
|
|
|
#include <boost/json/detail/value_to.hpp>
|
|
|
|
namespace boost {
|
|
namespace json {
|
|
|
|
/** Convert a @ref value to an object of type `T`.
|
|
|
|
This function attempts to convert a @ref value
|
|
to `T` using
|
|
|
|
@li one of @ref value's accessors, or
|
|
|
|
@li a library-provided generic conversion, or
|
|
|
|
@li a user-provided overload of `tag_invoke`.
|
|
|
|
Out of the box the function supports types satisfying
|
|
<a href="https://en.cppreference.com/w/cpp/named_req/SequenceContainer"><em>SequenceContainer</em></a>,
|
|
arrays, arithmetic types, `bool`, `std::tuple`, `std::pair`,
|
|
`std::variant`, `std::optional`, `std::monostate`, and `std::nullopt_t`.
|
|
|
|
Conversion of other types is done by calling an overload of `tag_invoke`
|
|
found by argument-dependent lookup. Its signature should be similar to:
|
|
|
|
@code
|
|
template< class FullContext >
|
|
T tag_invoke( value_to_tag<T>, const value&, const Context& , const FullContext& );
|
|
@endcode
|
|
|
|
or
|
|
|
|
@code
|
|
T tag_invoke( value_to_tag<T>, const value&, const Context& );
|
|
@endcode
|
|
|
|
or
|
|
|
|
@code
|
|
result<T> tag_invoke( value_to_tag<T>, const value& );
|
|
@endcode
|
|
|
|
The overloads are checked for existence in that order and the first that
|
|
matches will be selected. <br>
|
|
|
|
The object returned by the function call is returned by @ref value_to as
|
|
the result of the conversion. <br>
|
|
|
|
The `ctx` argument can be used either as a tag type to provide conversions
|
|
for third-party types, or to pass extra data to the conversion function.
|
|
|
|
@par Constraints
|
|
@code
|
|
! std::is_reference< T >::value
|
|
@endcode
|
|
|
|
@par Exception Safety
|
|
Strong guarantee.
|
|
|
|
@tparam T The type to convert to.
|
|
|
|
@tparam Context The type of context passed to the conversion function.
|
|
|
|
@returns `jv` converted to `result<T>`.
|
|
|
|
@param jv The @ref value to convert.
|
|
|
|
@param ctx Context passed to the conversion function.
|
|
|
|
@see @ref value_to_tag, @ref value_from,
|
|
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1895r0.pdf">
|
|
tag_invoke: A general pattern for supporting customisable functions</a>
|
|
*/
|
|
template< class T, class Context >
|
|
T
|
|
value_to( value const& jv, Context const& ctx )
|
|
{
|
|
BOOST_STATIC_ASSERT(! std::is_reference<T>::value);
|
|
using bare_T = detail::remove_cvref<T>;
|
|
BOOST_STATIC_ASSERT(detail::conversion_round_trips<
|
|
Context, bare_T, detail::value_to_conversion>::value);
|
|
using cat = detail::value_to_category<Context, bare_T>;
|
|
return detail::value_to_impl( cat(), value_to_tag<bare_T>(), jv, ctx );
|
|
}
|
|
|
|
/** Convert a @ref value to an object of type `T`.
|
|
|
|
This function attempts to convert a @ref value
|
|
to `T` using
|
|
|
|
@li one of @ref value's accessors, or
|
|
|
|
@li a library-provided generic conversion, or
|
|
|
|
@li a user-provided overload of `tag_invoke`.
|
|
|
|
Out of the box the function supports types satisfying
|
|
<a href="https://en.cppreference.com/w/cpp/named_req/SequenceContainer"><em>SequenceContainer</em></a>,
|
|
arrays, arithmetic types, `bool`, `std::tuple`, `std::pair`,
|
|
`std::variant`, `std::optional`, `std::monostate`, and `std::nullopt_t`.
|
|
|
|
Conversion of other types is done by calling an overload of `tag_invoke`
|
|
found by argument-dependent lookup. Its signature should be similar to:
|
|
|
|
@code
|
|
T tag_invoke( value_to_tag<T>, const value& );
|
|
@endcode
|
|
|
|
The object returned by the function call is
|
|
returned by @ref value_to as the result of the
|
|
conversion.
|
|
|
|
@par Constraints
|
|
@code
|
|
! std::is_reference< T >::value
|
|
@endcode
|
|
|
|
@par Exception Safety
|
|
Strong guarantee.
|
|
|
|
@tparam T The type to convert to.
|
|
|
|
@returns `jv` converted to `T`.
|
|
|
|
@param jv The @ref value to convert.
|
|
|
|
@see @ref value_to_tag, @ref value_from,
|
|
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1895r0.pdf">
|
|
tag_invoke: A general pattern for supporting customisable functions</a>
|
|
*/
|
|
template<class T>
|
|
T
|
|
value_to(const value& jv)
|
|
{
|
|
return value_to<T>( jv, detail::no_context() );
|
|
}
|
|
|
|
/** Convert a @ref value to a @ref result of `T`.
|
|
|
|
This function attempts to convert a @ref value
|
|
to `result<T>` using
|
|
|
|
@li one of @ref value's accessors, or
|
|
|
|
@li a library-provided generic conversion, or
|
|
|
|
@li a user-provided overload of `tag_invoke`.
|
|
|
|
Out of the box the function supports types satisfying
|
|
<a href="https://en.cppreference.com/w/cpp/named_req/SequenceContainer"><em>SequenceContainer</em></a>,
|
|
arrays, arithmetic types, `bool`, `std::tuple`, `std::pair`,
|
|
`std::variant`, `std::optional`, `std::monostate`, and `std::nullopt_t`.
|
|
|
|
Conversion of other types is done by calling an overload of `tag_invoke`
|
|
found by argument-dependent lookup. Its signature should be similar to:
|
|
|
|
@code
|
|
template< class FullContext >
|
|
result<T> tag_invoke( try_value_to_tag<T>, const value&, const Context& , const FullContext& );
|
|
@endcode
|
|
|
|
or
|
|
|
|
@code
|
|
result<T> tag_invoke( try_value_to_tag<T>, const value&, const Context& );
|
|
@endcode
|
|
|
|
or
|
|
|
|
@code
|
|
result<T> tag_invoke( try_value_to_tag<T>, const value& );
|
|
@endcode
|
|
|
|
The overloads are checked for existence in that order and the first that
|
|
matches will be selected. <br>
|
|
|
|
If an error occurs during conversion, the result will store the error code
|
|
associated with the error. If an exception is thrown, the function will
|
|
attempt to retrieve the associated error code and return it, otherwise it
|
|
will return `error::exception`, unless the exception type is
|
|
`std::bad_alloc`, which will be allowed to propagate. <br>
|
|
|
|
The `ctx` argument can be used either as a tag type to provide conversions
|
|
for third-party types, or to pass extra data to the conversion function.
|
|
|
|
@par Constraints
|
|
@code
|
|
! std::is_reference< T >::value
|
|
@endcode
|
|
|
|
@par Exception Safety
|
|
Strong guarantee.
|
|
|
|
@tparam T The type to convert to.
|
|
|
|
@tparam Context The type of context passed to the conversion function.
|
|
|
|
@param jv The @ref value to convert.
|
|
|
|
@param ctx Context passed to the conversion function.
|
|
|
|
@returns `jv` converted to `result<T>`.
|
|
|
|
@see @ref value_to_tag, @ref value_to, @ref value_from,
|
|
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1895r0.pdf">
|
|
tag_invoke: A general pattern for supporting customisable functions</a>
|
|
*/
|
|
template< class T, class Context >
|
|
typename result_for<T, value>::type
|
|
try_value_to( value const& jv, Context const& ctx )
|
|
{
|
|
BOOST_STATIC_ASSERT(! std::is_reference<T>::value);
|
|
using bare_T = detail::remove_cvref<T>;
|
|
BOOST_STATIC_ASSERT(detail::conversion_round_trips<
|
|
Context, bare_T, detail::value_to_conversion>::value);
|
|
using cat = detail::value_to_category<Context, bare_T>;
|
|
return detail::value_to_impl(
|
|
cat(), try_value_to_tag<bare_T>(), jv, ctx );
|
|
}
|
|
|
|
/** Convert a @ref value to a @ref result of `T`.
|
|
|
|
This function attempts to convert a @ref value
|
|
to `result<T>` using
|
|
|
|
@li one of @ref value's accessors, or
|
|
|
|
@li a library-provided generic conversion, or
|
|
|
|
@li a user-provided overload of `tag_invoke`.
|
|
|
|
Out of the box the function supports types satisfying
|
|
<a href="https://en.cppreference.com/w/cpp/named_req/SequenceContainer"><em>SequenceContainer</em></a>,
|
|
arrays, arithmetic types, `bool`, `std::tuple`, `std::pair`,
|
|
`std::variant`, `std::optional`, `std::monostate`, and `std::nullopt_t`.
|
|
|
|
Conversion of other types is done by calling an overload of `tag_invoke`
|
|
found by argument-dependent lookup. Its signature should be similar to:
|
|
|
|
@code
|
|
result<T> tag_invoke( try_value_to_tag<T>, const value& );
|
|
@endcode
|
|
|
|
If an error occurs during conversion, the result will store the error code
|
|
associated with the error. If an exception is thrown, the function will
|
|
attempt to retrieve the associated error code and return it, otherwise it
|
|
will return `error::exception`, unless the exception type is
|
|
`std::bad_alloc`, which will be allowed to propagate.
|
|
|
|
@par Constraints
|
|
@code
|
|
! std::is_reference< T >::value
|
|
@endcode
|
|
|
|
@par Exception Safety
|
|
Strong guarantee.
|
|
|
|
@tparam T The type to convert to.
|
|
|
|
@param jv The @ref value to convert.
|
|
|
|
@returns `jv` converted to `result<T>`.
|
|
|
|
@see @ref value_to_tag, @ref value_to, @ref value_from,
|
|
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1895r0.pdf">
|
|
tag_invoke: A general pattern for supporting customisable functions</a>
|
|
*/
|
|
template<class T>
|
|
typename result_for<T, value>::type
|
|
try_value_to(const value& jv)
|
|
{
|
|
return try_value_to<T>( jv, detail::no_context() );
|
|
}
|
|
|
|
/** Convert a @ref value to an object of type `T`.
|
|
|
|
This overload is **deleted** and participates in overload resolution only
|
|
when `U` is not @ref value. The overload exists to prevent unintented
|
|
creation of temporary @ref value instances, e.g.
|
|
|
|
@code
|
|
auto flag = value_to<bool>(true);
|
|
@endcode
|
|
*/
|
|
template<class T, class U
|
|
#ifndef BOOST_JSON_DOCS
|
|
, class = typename std::enable_if<!std::is_same<U, value>::value>::type
|
|
#endif
|
|
>
|
|
T
|
|
value_to(U const& jv) = delete;
|
|
|
|
/** Determine a @ref value can be converted to `T`.
|
|
|
|
If @ref value can be converted to `T` via a
|
|
call to @ref value_to, the static data member `value`
|
|
is defined as `true`. Otherwise, `value` is
|
|
defined as `false`.
|
|
|
|
@see @ref value_to
|
|
*/
|
|
#ifdef BOOST_JSON_DOCS
|
|
template<class T>
|
|
using has_value_to = __see_below__;
|
|
#else
|
|
template<class T>
|
|
using has_value_to = detail::can_convert<
|
|
detail::remove_cvref<T>, detail::value_to_conversion>;
|
|
#endif
|
|
|
|
} // namespace json
|
|
} // namespace boost
|
|
|
|
#endif
|