298 lines
8.7 KiB
C++
298 lines
8.7 KiB
C++
//
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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_FROM_HPP
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#define BOOST_JSON_VALUE_FROM_HPP
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#include <boost/json/detail/value_from.hpp>
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namespace boost {
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namespace json {
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/** Convert an object of type `T` to @ref value.
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This function attempts to convert an object
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of type `T` to @ref value using
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@li one of @ref value's constructors,
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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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void tag_invoke( value_from_tag, value&, T, const Context& , const FullContext& );
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@endcode
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or
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@code
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void tag_invoke( value_from_tag, value&, T, const Context& );
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@endcode
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or
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@code
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void tag_invoke( value_from_tag, value&, T );
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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 `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 Exception Safety
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Strong guarantee.
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@tparam T The type of the object to convert.
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@tparam Context The type of context passed to the conversion function.
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@param t The object to convert.
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@param ctx Context passed to the conversion function.
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@param jv @ref value out parameter.
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@see @ref value_from_tag, @ref value_to,
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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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void
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value_from(
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T&& t,
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Context const& ctx,
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value& jv)
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{
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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_from_conversion>::value);
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using cat = detail::value_from_category<Context, bare_T>;
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detail::value_from_impl( cat(), jv, std::forward<T>(t), ctx );
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}
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/** Convert an object of type `T` to @ref value.
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This function attempts to convert an object
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of type `T` to @ref value using
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@li one of @ref value's constructors,
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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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void tag_invoke( value_from_tag, value&, T, const Context& , const FullContext& );
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@endcode
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or
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@code
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void tag_invoke( value_from_tag, value&, T, const Context& );
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@endcode
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or
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@code
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void tag_invoke( value_from_tag, value&, T );
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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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A @ref value constructed with the @ref storage_ptr passed to
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@ref value_from is passed as the second argument to ensure that the memory
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resource is correctly propagated.
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@par Exception Safety
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Strong guarantee.
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@tparam T The type of the object to convert.
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@tparam Context The type of context passed to the conversion function.
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@returns `t` converted to @ref value.
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@param t The object to convert.
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@param ctx Context passed to the conversion function.
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@param sp A storage pointer referring to the memory resource
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to use for the returned @ref value. The default argument for this
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parameter is `{}`.
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@see @ref value_from_tag, @ref value_to,
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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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#ifndef BOOST_JSON_DOCS
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typename std::enable_if<
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!std::is_same< detail::remove_cvref<Context>, storage_ptr >::value &&
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!std::is_same< detail::remove_cvref<Context>, value >::value,
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value >::type
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#else
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value
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#endif
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value_from(
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T&& t,
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Context const& ctx,
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storage_ptr sp = {})
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{
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value jv(std::move(sp));
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value_from( static_cast<T&&>(t), ctx, jv );
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return jv;
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}
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/** Convert an object of type `T` to @ref value.
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This function attempts to convert an object
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of type `T` to @ref value using
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@li one of @ref value's constructors,
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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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void tag_invoke( value_from_tag, value&, T );
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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 of the object to convert.
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@param t The object to convert.
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@param jv @ref value out parameter.
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@see @ref value_from_tag, @ref value_to,
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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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void
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value_from(
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T&& t,
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value& jv)
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{
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value_from( static_cast<T&&>(t), detail::no_context(), jv );
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}
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/** Convert an object of type `T` to @ref value.
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This function attempts to convert an object
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of type `T` to @ref value using
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@li one of @ref value's constructors,
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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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void tag_invoke( value_from_tag, value&, T );
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@endcode
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A @ref value constructed
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with the @ref storage_ptr passed to @ref value_from is
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passed as the second argument to ensure that the memory
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resource is correctly propagated.
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@par Exception Safety
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Strong guarantee.
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@tparam T The type of the object to convert.
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@returns `t` converted to @ref value.
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@param t The object to convert.
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@param sp A storage pointer referring to the memory resource
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to use for the returned @ref value. The default argument for this
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parameter is `{}`.
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@see @ref value_from_tag, @ref value_to,
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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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value
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value_from(
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T&& t,
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storage_ptr sp = {})
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{
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return value_from(
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static_cast<T&&>(t), detail::no_context(), std::move(sp) );
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}
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/** Determine if `T` can be converted to @ref value.
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If `T` can be converted to @ref value via a
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call to @ref value_from, 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_from
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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_from = __see_below__;
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#else
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template<class T>
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using has_value_from = detail::can_convert<
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detail::remove_cvref<T>, detail::value_from_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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