update boost
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linx64/include/boost/json/value_to.hpp
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327
linx64/include/boost/json/value_to.hpp
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//
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// Copyright (c) 2019 Vinnie Falco (vinnie.falco@gmail.com)
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// Copyright (c) 2020 Krystian Stasiowski (sdkrystian@gmail.com)
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// Copyright (c) 2022 Dmitry Arkhipov (grisumbras@gmail.com)
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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// Official repository: https://github.com/boostorg/json
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//
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#ifndef BOOST_JSON_VALUE_TO_HPP
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#define BOOST_JSON_VALUE_TO_HPP
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#include <boost/json/detail/value_to.hpp>
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namespace boost {
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namespace json {
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/** Convert a @ref value to an object of type `T`.
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This function attempts to convert a @ref value
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to `T` using
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@li one of @ref value's accessors, or
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@li a library-provided generic conversion, or
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@li a user-provided overload of `tag_invoke`.
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Out of the box the function supports types satisfying
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<a href="https://en.cppreference.com/w/cpp/named_req/SequenceContainer"><em>SequenceContainer</em></a>,
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arrays, arithmetic types, `bool`, `std::tuple`, `std::pair`,
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`std::variant`, `std::optional`, `std::monostate`, and `std::nullopt_t`.
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Conversion of other types is done by calling an overload of `tag_invoke`
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found by argument-dependent lookup. Its signature should be similar to:
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@code
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template< class FullContext >
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T tag_invoke( value_to_tag<T>, const value&, const Context& , const FullContext& );
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@endcode
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or
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@code
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T tag_invoke( value_to_tag<T>, const value&, const Context& );
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@endcode
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or
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@code
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result<T> tag_invoke( value_to_tag<T>, const value& );
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@endcode
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The overloads are checked for existence in that order and the first that
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matches will be selected. <br>
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The object returned by the function call is returned by @ref value_to as
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the result of the conversion. <br>
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The `ctx` argument can be used either as a tag type to provide conversions
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for third-party types, or to pass extra data to the conversion function.
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@par Constraints
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@code
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! std::is_reference< T >::value
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@endcode
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@par Exception Safety
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Strong guarantee.
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@tparam T The type to convert to.
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@tparam Context The type of context passed to the conversion function.
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@returns `jv` converted to `result<T>`.
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@param jv The @ref value to convert.
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@param ctx Context passed to the conversion function.
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@see @ref value_to_tag, @ref value_from,
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<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1895r0.pdf">
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tag_invoke: A general pattern for supporting customisable functions</a>
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*/
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template< class T, class Context >
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T
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value_to( value const& jv, Context const& ctx )
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{
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BOOST_STATIC_ASSERT(! std::is_reference<T>::value);
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using bare_T = detail::remove_cvref<T>;
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BOOST_STATIC_ASSERT(detail::conversion_round_trips<
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Context, bare_T, detail::value_to_conversion>::value);
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using cat = detail::value_to_category<Context, bare_T>;
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return detail::value_to_impl( cat(), value_to_tag<bare_T>(), jv, ctx );
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}
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/** Convert a @ref value to an object of type `T`.
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This function attempts to convert a @ref value
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to `T` using
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@li one of @ref value's accessors, or
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@li a library-provided generic conversion, or
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@li a user-provided overload of `tag_invoke`.
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Out of the box the function supports types satisfying
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<a href="https://en.cppreference.com/w/cpp/named_req/SequenceContainer"><em>SequenceContainer</em></a>,
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arrays, arithmetic types, `bool`, `std::tuple`, `std::pair`,
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`std::variant`, `std::optional`, `std::monostate`, and `std::nullopt_t`.
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Conversion of other types is done by calling an overload of `tag_invoke`
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found by argument-dependent lookup. Its signature should be similar to:
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@code
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T tag_invoke( value_to_tag<T>, const value& );
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@endcode
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The object returned by the function call is
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returned by @ref value_to as the result of the
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conversion.
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@par Constraints
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@code
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! std::is_reference< T >::value
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@endcode
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@par Exception Safety
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Strong guarantee.
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@tparam T The type to convert to.
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@returns `jv` converted to `T`.
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@param jv The @ref value to convert.
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@see @ref value_to_tag, @ref value_from,
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<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1895r0.pdf">
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tag_invoke: A general pattern for supporting customisable functions</a>
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*/
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template<class T>
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T
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value_to(const value& jv)
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{
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return value_to<T>( jv, detail::no_context() );
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}
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/** Convert a @ref value to a @ref result of `T`.
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This function attempts to convert a @ref value
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to `result<T>` using
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@li one of @ref value's accessors, or
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@li a library-provided generic conversion, or
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@li a user-provided overload of `tag_invoke`.
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Out of the box the function supports types satisfying
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<a href="https://en.cppreference.com/w/cpp/named_req/SequenceContainer"><em>SequenceContainer</em></a>,
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arrays, arithmetic types, `bool`, `std::tuple`, `std::pair`,
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`std::variant`, `std::optional`, `std::monostate`, and `std::nullopt_t`.
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Conversion of other types is done by calling an overload of `tag_invoke`
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found by argument-dependent lookup. Its signature should be similar to:
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@code
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template< class FullContext >
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result<T> tag_invoke( try_value_to_tag<T>, const value&, const Context& , const FullContext& );
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@endcode
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or
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@code
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result<T> tag_invoke( try_value_to_tag<T>, const value&, const Context& );
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@endcode
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or
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@code
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result<T> tag_invoke( try_value_to_tag<T>, const value& );
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@endcode
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The overloads are checked for existence in that order and the first that
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matches will be selected. <br>
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If an error occurs during conversion, the result will store the error code
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associated with the error. If an exception is thrown, the function will
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attempt to retrieve the associated error code and return it, otherwise it
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will return `error::exception`, unless the exception type is
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`std::bad_alloc`, which will be allowed to propagate. <br>
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The `ctx` argument can be used either as a tag type to provide conversions
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for third-party types, or to pass extra data to the conversion function.
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@par Constraints
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@code
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! std::is_reference< T >::value
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@endcode
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@par Exception Safety
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Strong guarantee.
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@tparam T The type to convert to.
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@tparam Context The type of context passed to the conversion function.
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@param jv The @ref value to convert.
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@param ctx Context passed to the conversion function.
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@returns `jv` converted to `result<T>`.
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@see @ref value_to_tag, @ref value_to, @ref value_from,
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<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1895r0.pdf">
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tag_invoke: A general pattern for supporting customisable functions</a>
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*/
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template< class T, class Context >
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typename result_for<T, value>::type
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try_value_to( value const& jv, Context const& ctx )
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{
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BOOST_STATIC_ASSERT(! std::is_reference<T>::value);
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using bare_T = detail::remove_cvref<T>;
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BOOST_STATIC_ASSERT(detail::conversion_round_trips<
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Context, bare_T, detail::value_to_conversion>::value);
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using cat = detail::value_to_category<Context, bare_T>;
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return detail::value_to_impl(
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cat(), try_value_to_tag<bare_T>(), jv, ctx );
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}
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/** Convert a @ref value to a @ref result of `T`.
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This function attempts to convert a @ref value
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to `result<T>` using
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@li one of @ref value's accessors, or
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@li a library-provided generic conversion, or
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@li a user-provided overload of `tag_invoke`.
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Out of the box the function supports types satisfying
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<a href="https://en.cppreference.com/w/cpp/named_req/SequenceContainer"><em>SequenceContainer</em></a>,
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arrays, arithmetic types, `bool`, `std::tuple`, `std::pair`,
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`std::variant`, `std::optional`, `std::monostate`, and `std::nullopt_t`.
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Conversion of other types is done by calling an overload of `tag_invoke`
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found by argument-dependent lookup. Its signature should be similar to:
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@code
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result<T> tag_invoke( try_value_to_tag<T>, const value& );
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@endcode
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If an error occurs during conversion, the result will store the error code
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associated with the error. If an exception is thrown, the function will
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attempt to retrieve the associated error code and return it, otherwise it
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will return `error::exception`, unless the exception type is
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`std::bad_alloc`, which will be allowed to propagate.
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@par Constraints
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@code
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! std::is_reference< T >::value
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@endcode
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@par Exception Safety
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Strong guarantee.
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@tparam T The type to convert to.
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@param jv The @ref value to convert.
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@returns `jv` converted to `result<T>`.
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@see @ref value_to_tag, @ref value_to, @ref value_from,
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<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1895r0.pdf">
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tag_invoke: A general pattern for supporting customisable functions</a>
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*/
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template<class T>
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typename result_for<T, value>::type
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try_value_to(const value& jv)
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{
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return try_value_to<T>( jv, detail::no_context() );
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}
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/** Convert a @ref value to an object of type `T`.
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This overload is **deleted** and participates in overload resolution only
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when `U` is not @ref value. The overload exists to prevent unintented
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creation of temporary @ref value instances, e.g.
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@code
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auto flag = value_to<bool>(true);
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@endcode
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*/
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template<class T, class U
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#ifndef BOOST_JSON_DOCS
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, class = typename std::enable_if<!std::is_same<U, value>::value>::type
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#endif
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>
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T
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value_to(U const& jv) = delete;
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/** Determine a @ref value can be converted to `T`.
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If @ref value can be converted to `T` via a
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call to @ref value_to, the static data member `value`
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is defined as `true`. Otherwise, `value` is
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defined as `false`.
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@see @ref value_to
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*/
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#ifdef BOOST_JSON_DOCS
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template<class T>
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using has_value_to = __see_below__;
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#else
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template<class T>
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using has_value_to = detail::can_convert<
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detail::remove_cvref<T>, detail::value_to_conversion>;
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#endif
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} // namespace json
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} // namespace boost
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#endif
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