forked from KPGPMC/furlang
369 lines
9.5 KiB
C++
369 lines
9.5 KiB
C++
#ifndef FURLANG_RESULT_HPP
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#define FURLANG_RESULT_HPP
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#include <exception>
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#include <ostream>
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#include <utility>
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namespace furlang {
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/**
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* @brief Bad result access exception.
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*/
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class bad_result_access : public std::exception {
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public:
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bad_result_access() = default;
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~bad_result_access() override = default;
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/**
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* @brief Move constructor.
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*/
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bad_result_access(bad_result_access&&) noexcept = default;
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/**
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* @brief Move constructor.
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*/
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bad_result_access& operator=(bad_result_access&&) noexcept = default;
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/**
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* @brief Copy constructor.
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*/
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bad_result_access(const bad_result_access&) = default;
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/**
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* @brief Copy constructor.
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*/
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bad_result_access& operator=(const bad_result_access&) = default;
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public:
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/**
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* @brief Returns a C-style string describing the cause of the error.
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*
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* @return The cause of the error.
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*/
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const char* what() const noexcept override { return "bad result access"; }
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};
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/**
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* @brief Result.
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*
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* Result stores either value or error.
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*
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* @tparam R Value type.
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* @tparam E Error type.
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*/
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template <typename R, typename E>
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class result {
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public:
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using value_type = std::remove_reference_t<R>; /**< Value type. */
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using value_reference = value_type&; /**< Value reference type. */
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using value_const_reference = const value_type&; /**< Value const reference type. */
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using value_pointer = value_type*; /**< Value pointer type. */
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using value_const_pointer = const value_type*; /**< Value const pointer type. */
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using error_type = std::remove_reference_t<E>; /**< Error type. */
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using error_reference = error_type&; /**< Error reference type. */
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using error_const_reference = const error_type&; /**< Error const reference type. */
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public:
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/**
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* @brief Construct a new result.
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*
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* @param value Value to copy.
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*/
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result(const value_type& value) { new (&m_value.result) value_type(value); }
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/**
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* @brief Construct a new result.
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*
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* @param value Value to move.
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*/
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result(value_type&& value) { new (&m_value.result) value_type(std::move(value)); }
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/**
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* @brief Construct a new result.
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*
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* @param args Variadic arguments to construct the value with.
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*/
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template <typename... Args>
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result(Args&&... args) {
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new (&m_value.result) value_type(std::forward<Args>(args)...);
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}
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/**
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* @brief Construct a new error result.
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*
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* @param error Error to copy.
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*/
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explicit result(const error_type& error)
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: m_error(true) {
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new (&m_value.error) error_type(error);
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}
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/**
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* @brief Construct a new error result.
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*
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* @param error Error to move.
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*/
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explicit result(error_type&& error)
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: m_error(true) {
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new (&m_value.error) error_type(std::move(error));
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}
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~result() {
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if (m_error) {
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m_value.error.~error_type();
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} else {
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m_value.result.~value_type();
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}
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}
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/**
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* @brief Move constructor.
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*/
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result(result&& other) noexcept
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: m_error(other.m_error) {
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if (m_error) {
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new (&m_value.error) error_type(std::move(other.m_value.error));
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} else {
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new (&m_value.result) value_type(std::move(other.m_value.result));
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}
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}
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/**
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* @brief Move constructor.
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*/
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result& operator=(result&& other) noexcept {
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if (this == &other) return *this;
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m_error = other.m_error;
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if (m_error) {
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new (&m_value.error) error_type(std::move(other.m_value.error));
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} else {
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new (&m_value.result) value_type(std::move(other.m_value.result));
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}
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return *this;
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}
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/**
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* @brief Copy constructor.
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*/
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result(const result& other)
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: m_error(other.m_error) {
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if (m_error) {
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new (&m_value.error) error_type(other.m_value.error);
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} else {
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new (&m_value.result) value_type(other.m_value.result);
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}
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}
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/**
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* @brief Copy constructor.
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*/
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result& operator=(const result& other) {
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if (this == &other) return *this;
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m_error = other.m_error;
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if (m_error) {
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new (&m_value.error) error_type(other.m_value.error);
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} else {
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new (&m_value.result) value_type(other.m_value.result);
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}
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return *this;
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}
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public:
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/**
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* @brief Checks if this result contains a value.
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*
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* @return true if contains a value.
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*/
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operator bool() const { return !m_error; }
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/**
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* @brief Checks if this result contains an error.
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*
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* @return true if contains an error.
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*/
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bool operator!() const { return m_error; }
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/**
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* @brief Compares two results for equality.
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*
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* @param rhs Result to compare against.
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* @return true if the results are equal.
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*/
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bool operator==(const result& rhs) const {
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return m_error == rhs.m_error && m_error ? m_value.error == rhs.m_value.error
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: m_value.result == rhs.m_value.result;
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}
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/**
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* @brief Compares two results for inequality.
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*
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* @param rhs Result to compare against.
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* @return true if the results are not equal.
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*/
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bool operator!=(const result& rhs) const { return !this->operator==(rhs); }
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/**
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* @brief Compares a result with a value for equality.
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*
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* @param rhs Value to compare against.
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* @return true if the values are equal.
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*/
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bool operator==(const value_type& rhs) const { return !m_error && m_value.result == rhs; }
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/**
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* @brief Compares a result with a value for inequality.
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*
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* @param rhs Value to compare against.
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* @return true if the values are not equal.
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*/
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bool operator!=(const value_type& rhs) const { return !this->operator==(rhs); }
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/**
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* @brief Prints a result to an output stream.
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*
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* @param os Output stream.
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* @param result Result to print.
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* @return The output stream.
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*/
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friend std::ostream& operator<<(std::ostream& os, const result& result) {
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return result.has_value() ? os << result.value() : os << result.error();
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}
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/**
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* @brief Returns a reference to value.
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*
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* @return Reference to the value.
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*/
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value_reference operator*() { return value(); }
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/**
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* @brief Returns a reference to value.
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*
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* @return Const reference to the value.
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*/
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value_const_reference operator*() const { return value(); }
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/**
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* @brief Returns a pointer to value.
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*
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* @return Pointer to the value.
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*/
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value_pointer operator->() { return &value(); }
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/**
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* @brief Returns a pointer to value.
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*
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* @return Const pointer to the value.
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*/
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value_const_pointer operator->() const { return &value(); }
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public:
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/**
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* @brief Checks if this result has a value.
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*
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* @return true if has a value.
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*/
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bool has_value() const { return !m_error; }
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/**
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* @brief Checks if this result has an error.
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*
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* @return true if has an error.
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*/
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bool has_error() const { return m_error; }
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/**
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* @brief Returns a reference to value.
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*
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* @return Reference to the value.
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*/
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value_reference value() {
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if (m_error) throw bad_result_access();
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return m_value.result;
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}
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/**
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* @brief Returns a reference to value.
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*
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* @return Const reference to the value.
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*/
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value_const_reference value() const {
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if (m_error) throw bad_result_access();
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return m_value.result;
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}
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/**
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* @brief Returns a reference to error.
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*
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* @return Reference to the error.
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*/
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error_reference error() {
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if (!m_error) throw bad_result_access();
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return m_value.error;
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}
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/**
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* @brief Returns a reference to error.
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*
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* @return Const reference to the error.
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*/
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error_const_reference error() const {
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if (!m_error) throw bad_result_access();
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return m_value.error;
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}
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public:
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/**
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* @brief Sets this results value.
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*
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* @param value Value to copy.
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*/
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void set_value(const value_type& value) {
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if (m_error) m_value.error.~error_type();
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new (&m_value.result) value_type(value);
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}
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/**
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* @brief Sets this results value.
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*
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* @param value Value to move.
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*/
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void set_value(value_type&& value) {
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if (m_error) m_value.error.~error_type();
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new (&m_value.result) value_type(std::move(value));
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}
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/**
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* @brief Sets this results error.
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*
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* @param error Error to copy.
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*/
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void set_error(const error_type& error) {
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if (!m_error) m_value.result.~value_type();
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new (&m_value.error) error_type(error);
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}
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/**
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* @brief Sets this results error.
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*
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* @param error Error to move.
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*/
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void set_error(error_type&& error) {
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if (!m_error) m_value.result.~value_type();
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new (&m_value.error) error_type(std::move(error));
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}
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private:
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union value {
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value_type result;
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error_type error;
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value() {}
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~value() {}
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value(value&&) noexcept {}
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value& operator=(value&&) noexcept {}
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value(const value&) {}
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value& operator=(const value&) {}
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} m_value;
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bool m_error = false;
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};
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} // namespace furlang
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#endif // FURLANG_RESULT_HPP
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