Add result to furlang

Signed-off-by: CHatingPython <chatingpython@gmail.com>
2026-05-31 11:40:39 +02:00
parent 737f637a38
commit 82c9037a6a
2 changed files with 146 additions and 0 deletions
@@ -0,0 +1,143 @@
+#ifndef FURLANG_RESULT_HPP
+#define FURLANG_RESULT_HPP
+
+#include <exception>
+#include <utility>
+
+namespace furlang {
+
+class bad_result_access : public std::exception {
+public:
+    bad_result_access()           = default;
+    ~bad_result_access() override = default;
+
+    bad_result_access(bad_result_access&&) noexcept            = default;
+    bad_result_access& operator=(bad_result_access&&) noexcept = default;
+    bad_result_access(const bad_result_access&)                = default;
+    bad_result_access& operator=(const bad_result_access&)     = default;
+public:
+    const char* what() const noexcept override { return "bad result access"; }
+};
+
+template <typename R, typename E>
+class result {
+public:
+    using value_type            = std::remove_reference_t<R>;
+    using value_reference       = value_type&;
+    using value_const_reference = const value_type&;
+    using value_pointer         = value_type*;
+    using value_const_pointer   = const value_type*;
+    using error_type            = std::remove_reference_t<E>;
+    using error_reference       = error_type&;
+    using error_const_reference = const error_type&;
+public:
+    result(const value_type& value) { new (&m_value.result) value_type(value); }
+
+    result(value_type&& value) { new (&m_value.result) value_type(std::move(value)); }
+
+    template <typename... Args>
+    result(Args&&... args) {
+        new (&m_value.result) value_type(std::forward<Args>(args)...);
+    }
+
+    explicit result(const error_type& error)
+      : m_error(true) {
+        m_value.error = error;
+    }
+
+    explicit result(error_type&& error)
+      : m_error(true) {
+        m_value.error = std::move(error);
+    }
+
+    ~result() {
+        if (m_error) {
+            m_value.error.~error_type();
+        } else {
+            m_value.result.~value_type();
+        }
+    }
+
+    result(result&& other) noexcept {}
+
+    result& operator=(result&& other) noexcept {
+        if (this == &other) return *this;
+        return *this;
+    }
+
+    result(const result& other) {}
+
+    result& operator=(const result& other) {
+        if (this == &other) return *this;
+        return *this;
+    }
+public:
+         operator bool() const { return !m_error; }
+    bool operator!() const { return m_error; }
+
+    bool operator==(const result& rhs) const {
+        return m_error == rhs.m_error && m_error ? m_value.error == rhs.m_value.error
+                                                 : m_value.result == rhs.m_value.result;
+    }
+
+    bool operator!=(const result& rhs) const { return !this->operator==(rhs); }
+
+    value_reference       operator*() { return value(); }
+    value_const_reference operator*() const { return value(); }
+
+    value_pointer       operator->() { return &value(); }
+    value_const_pointer operator->() const { return &value(); }
+public:
+    bool has_value() const { return !m_error; }
+    bool has_error() const { return m_error; }
+
+    value_reference value() {
+        if (m_error) throw bad_result_access();
+        return m_value.result;
+    }
+
+    value_const_reference value() const {
+        if (m_error) throw bad_result_access();
+        return m_value.result;
+    }
+
+    error_reference error() {
+        if (!m_error) throw bad_result_access();
+        return m_value.error;
+    }
+
+    error_const_reference error() const {
+        if (!m_error) throw bad_result_access();
+        return m_value.error;
+    }
+public:
+    void set_value(const value_type& value) {
+        if (m_error) m_value.error.~error_type();
+        new (&m_value.result) value_type(value);
+    }
+
+    void set_value(value_type&& value) {
+        if (m_error) m_value.error.~error_type();
+        new (&m_value.result) value_type(std::move(value));
+    }
+
+    void set_error(const error_type& error) {
+        if (!m_error) m_value.result.~value_type();
+        new (&m_value.error) error_type(error);
+    }
+
+    void set_error(error_type&& error) {
+        if (!m_error) m_value.result.~value_type();
+        new (&m_value.error) error_type(std::move(error));
+    }
+private:
+    union value {
+        value_type result;
+        error_type error;
+    } m_value;
+    bool m_error = false;
+};
+
+} // namespace furlang
+
+#endif // FURLANG_RESULT_HPP