整理

include/boost/scope/error_code_checker.hpp

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+/*
+ * Distributed under the Boost Software License, Version 1.0.
+ * (See accompanying file LICENSE_1_0.txt or copy at
+ * https://www.boost.org/LICENSE_1_0.txt)
+ *
+ * Copyright (c) 2023 Andrey Semashev
+ */
+/*!
+ * \file scope/error_code_checker.hpp
+ *
+ * This header contains definition of \c error_code_checker type.
+ */
+
+#ifndef BOOST_SCOPE_ERROR_CODE_CHECKER_HPP_INCLUDED_
+#define BOOST_SCOPE_ERROR_CODE_CHECKER_HPP_INCLUDED_
+
+#include <boost/core/addressof.hpp>
+#include <boost/scope/detail/config.hpp>
+#include <boost/scope/detail/header.hpp>
+
+#ifdef BOOST_HAS_PRAGMA_ONCE
+#pragma once
+#endif
+
+namespace boost {
+namespace scope {
+
+/*!
+ * \brief A predicate for checking whether an error code indicates error.
+ *
+ * The predicate captures a reference to an external error code object, which it
+ * tests for an error indication when called. The error code object must remain
+ * valid for the whole lifetime duration of the predicate.
+ *
+ * For an error code object `ec`, an expression `!ec` must be valid, never throw exceptions,
+ * and return a value contextually convertible to `bool`. If the returned value converts
+ * to `false`, then this is taken as an error indication, and the predicate returns `true`.
+ * Otherwise, the predicate returns `false`.
+ *
+ * A few examples of error code types:
+ *
+ * \li `std::error_code` or `boost::system::error_code`,
+ * \li `std::expected`, `boost::outcome_v2::basic_outcome` or `boost::outcome_v2::basic_result`,
+ * \li `int`, where the value of 0 indicates no error,
+ * \li `bool`, where the value of `false` indicates no error,
+ * \li `T*`, where a null pointer indicates no error.
+ *
+ * \tparam ErrorCode Error code type.
+ */
+template< typename ErrorCode >
+class error_code_checker
+{
+public:
+    //! Predicate result type
+    using result_type = bool;
+
+private:
+    ErrorCode* m_error_code;
+
+public:
+    /*!
+     * \brief Constructs the predicate.
+     *
+     * Upon construction, the predicate saves a reference to the external error code object.
+     * The referenced object must remain valid for the whole lifetime duration of the predicate.
+     *
+     * **Throws:** Nothing.
+     */
+    explicit error_code_checker(ErrorCode& ec) noexcept :
+        m_error_code(boost::addressof(ec))
+    {
+    }
+
+    /*!
+     * \brief Checks if the error code indicates error.
+     *
+     * **Throws:** Nothing.
+     *
+     * \returns As if `!!ec`, where `ec` is the error code object passed to the predicate constructor.
+     */
+    result_type operator()() const noexcept
+    {
+        return !!(*m_error_code);
+    }
+};
+
+/*!
+ * \brief Creates a predicate for checking whether an exception is being thrown
+ *
+ * **Throws:** Nothing.
+ */
+template< typename ErrorCode >
+inline error_code_checker< ErrorCode > check_error_code(ErrorCode& ec) noexcept
+{
+    return error_code_checker< ErrorCode >(ec);
+}
+
+} // namespace scope
+} // namespace boost
+
+#include <boost/scope/detail/footer.hpp>
+
+#endif // BOOST_SCOPE_ERROR_CODE_CHECKER_HPP_INCLUDED_