feat: add Rust env namespace

src/yycc/rust/env.hpp

@@ -0,0 +1,62 @@
+#pragma once
+#include <string>
+#include <string_view>
+#include <expected>
+
+/**
+ * @brief The namespace providing environment variable operations.
+ * @details
+ * When I programming with Rust, I was astonished that
+ * Rust standard library have so much robust environment variable operations.
+ * Oppositly, C++ STL still lake in this even in today.
+ *
+ * The functions manipulating environment variable is different in different OS.
+ * I create this namespace inspired from Rust standard library
+ * to glue all these things up and make a uniform interface.
+ */
+namespace yycc::rust::env {
+
+    /// @brief The error occurs in this module.
+    enum class EnvError {
+        NoSuchName,    ///< The variable with given name is not presented.
+        BadEncoding,   ///< Error when performing encoding convertion.
+        BadArithmetic, ///< Error when performing arithmetic operations.
+        BadCall,       ///< Error occurs when calling backend functions.
+        BadName,       ///< Given name is ill-formated (empty string or has "=" character).
+        NoMemory,      ///< No enough memory to finish this operation.
+    };
+
+    /// @brief The result type in this module.
+    template<typename T>
+    using EnvResult = std::expected<T, EnvError>;
+
+    /**
+     * @brief Get the value of given environment variable name.
+     * @param[in] name The name of environment variable
+     * @return Gotten value, or error occurs.
+     */
+    EnvResult<std::u8string> get_var(const std::u8string_view& name);
+
+    /**
+     * @brief Set the value of given environment variable name.
+     * @details
+     * If there is no such name variable presented in environment,
+     * a new variable will be created,
+     * otherwise, new value will overwrite old value.
+     * @param[in] name The name of environment variable
+     * @param[in] value The value to be written into.
+     * @return Nothing or error occurs.
+     */
+    EnvResult<void> set_var(const std::u8string_view& name, const std::u8string_view& value);
+
+    /**
+     * @brief Delete environment variable with given name.
+     * @details
+     * If given variable is not presented in environment,
+     * this function will NOT return error.
+     * @param[in] name The name of environment variable
+     * @return Nothing, or error occurs.
+     */
+    EnvResult<void> del_var(const std::u8string_view& name);
+
+} // namespace yycc::rust::env