159 lines
4.1 KiB
C++
159 lines
4.1 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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//
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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/config.hpp>
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#include <boost/json/value.hpp>
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#include <boost/json/detail/value_from.hpp>
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BOOST_JSON_NS_BEGIN
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/** Customization point tag.
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This tag type is used by the function
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@ref value_from to select overloads
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of `tag_invoke`.
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@note This type is empty; it has no members.
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@see @ref value_from, @ref value_to, @ref value_to_tag,
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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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#ifndef BOOST_JSON_DOCS
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struct value_from_tag;
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#else
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// VFALCO Doc toolchain doesn't like
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// forward declared ordinary classes.
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struct value_from_tag {};
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#endif
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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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In all cases, the conversion is done by calling
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an overload of `tag_invoke` found by argument-dependent
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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 detail::value_from_impl(
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std::forward<T>(t), std::move(sp));
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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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In all cases, the conversion is done by calling
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an overload of `tag_invoke` found by argument-dependent
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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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jv = detail::value_from_impl(
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std::forward<T>(t), jv.storage());
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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, class>
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struct has_value_from : std::false_type { };
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template<class T>
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struct has_value_from<T, detail::void_t<
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decltype(detail::value_from_impl(std::declval<T&&>(),
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std::declval<storage_ptr>()))>>
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: std::true_type { };
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#endif
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BOOST_JSON_NS_END
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#endif
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