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Added thirdparty: boost library
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Viacheslav Demydiuk
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//
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// Copyright (c) 2019 Vinnie Falco (vinnie.falco@gmail.com)
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// Copyright (c) 2022 Dmitry Arkhipov (grisumbras@yandex.ru)
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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_SYSTEM_ERROR_HPP
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#define BOOST_JSON_SYSTEM_ERROR_HPP
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#include <boost/json/detail/config.hpp>
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#include <boost/json/fwd.hpp>
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#include <boost/assert/source_location.hpp>
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#include <boost/system/error_code.hpp>
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#include <boost/system/result.hpp>
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#include <boost/system/system_error.hpp>
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namespace boost {
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namespace json {
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/// The type of error code used by the library.
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using error_code = boost::system::error_code;
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/// The type of error category used by the library.
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using error_category = boost::system::error_category;
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/// The type of error condition used by the library.
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using error_condition = boost::system::error_condition;
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/// The type of system error thrown by the library.
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using system_error = boost::system::system_error;
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/** The type of result returned by library functions
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This is an alias template used as the return type for functions that can
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either return a value, or fail with an error code. This is a brief
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synopsis of the type:
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@par Declaration
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@code
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template< class T >
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class result
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{
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public:
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// Return true if the result contains an error
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constexpr bool has_error() const noexcept;
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// These two return true if the result contains a value
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constexpr bool has_value() const noexcept;
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constexpr explicit operator bool() const noexcept;
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// Return the value or throw an exception if has_value() == false
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constexpr T& value();
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constexpr T const& value() const;
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// Return the value, assuming the result contains it
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constexpr T& operator*();
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constexpr T const& operator*() const;
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// Return the error, which is default constructed if has_error() == false
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constexpr error_code error() const noexcept;
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...more
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};
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@endcode
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@par Usage
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Given the function @ref try_value_to with this signature:
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@code
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template< class T>
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result< T > try_value_to( const value& jv );
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@endcode
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The following statement captures the value in a variable upon success,
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otherwise throws:
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@code
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int n = try_value_to<int>( jv ).value();
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@endcode
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This statement captures the result in a variable and inspects the error
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condition:
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@code
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result< int > r = try_value_to<int>( jv );
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if( r )
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std::cout << *r;
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else
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std::cout << r.error();
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@endcode
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@note For a full synopsis of the type, please see the corresponding
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documentation in Boost.System.
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@tparam T The type of value held by the result.
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*/
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template< class T >
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using result = boost::system::result<T>;
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/**
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Helper trait that returns @ref result
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The primary template is an incomplete type. The library provides a partial
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specialisation `result_for<T1, value>`, that has nested type alias `type`
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that aliases the type `result<T1>`.
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The purpose of this trait is to let users provide non-throwing conversions
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for their types without creating a physical dependency on Boost.Json. For
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example:
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@code
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namespace boost
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{
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namespace json
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{
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template<class T>
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struct value_to_tag;
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template<class T1, class T2>
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struct result_for;
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}
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}
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namespace mine
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{
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class my_class;
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...
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template<class JsonValue>
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boost::json::result_for<my_class, JsonValue>
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tag_invoke(boost::json::try_value_to_tag<my_class>, const JsonValue& jv)
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{ ... }
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}
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@endcode
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@see @ref try_value_to, @ref try_value_to_tag
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*/
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template <class T1, class T2>
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struct result_for;
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/** Create @ref result storing a portable error code
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This function constructs a `result<T>` that stores @ref error_code with
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`value()` equal to `e` and `category()` equal to
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`boost::system::generic_category()`. <br>
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The main use for this function is in implementation of functions returning
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@ref result, without including `boost/json/system_error.hpp` or even
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`<system_error>`. In particular, it may be useful for customizations of
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@ref try_value_to without creating a physical dependency on Boost.JSON.
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For example:
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@code
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#include <cerrno>
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#include <boost/assert/source_location.hpp>
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namespace boost
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{
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namespace json
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{
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class value;
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template<class T>
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struct try_value_to_tag;
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template<class T1, class T2>
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struct result_for;
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template <class T>
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typename result_for<T, value>::type
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result_from_errno(int e, boost::source_location const* loc) noexcept
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}
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}
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namespace mine
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{
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class my_class;
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...
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template<class JsonValue>
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boost::json::result_for<my_class, JsonValue>
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tag_invoke(boost::json::try_value_to_tag<my_class>, const JsonValue& jv)
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{
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BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
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if( !jv.is_null() )
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return boost::json::result_from_errno<my_class>(EINVAL, &loc);
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return my_class();
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}
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}
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@endcode
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@par Exception Safety
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Does not throw exceptions.
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@tparam T The value type of returned `result`.
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@param e The error value.
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@param loc The error location.
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@returns @ref error_code with `value()` equal to `e` and `category()` equal
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to `boost::system::generic_category()`.
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@see @ref try_value_to_tag, @ref try_value_to, @ref result_for,
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<a href="https://www.boost.org/doc/libs/develop/libs/system/doc/html/system.html#ref_generic_category">
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`boost::system::generic_category`</a>,
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<a href="https://www.boost.org/doc/libs/master/libs/assert/doc/html/assert.html#source_location_support">
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`boost::source_location`</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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result_from_errno(int e, boost::source_location const* loc) noexcept
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{
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error_code ec(e, system::generic_category(), loc);
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return {system::in_place_error, ec};
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}
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} // namespace json
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} // namespace boost
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#endif
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