feat: add lost functions for env namespace.

- add some lost functions for env namespace according to Rust std library. hiwever some functions are not implemented.
- change some function's signatures located in env namespace.
- reduce some useless error kine in env namespace.

src/yycc/env.hpp

@@ -1,11 +1,11 @@
 #pragma once
 #include <string>
 #include <string_view>
+#include <filesystem>
 #include <expected>
 
 /**
  * @brief The namespace providing runtime environment operations.
-
  * @details
  * When I programming with Rust, I was astonished that
  * Rust standard library have so much robust environment-related operations,
@@ -20,18 +20,24 @@ namespace yycc::env {
 
     /// @brief The error occurs in environment variable operations.
     enum class VarError {
+        SysCall,       ///< Error occurs when calling backend functions.
         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).
+        BadEncoding,   ///< Error when performing encoding convertion.
         NoMemory,      ///< No enough memory to finish this operation.
+        Others,        ///< Any other error types.
     };
 
     /// @brief The result type in environment variable operations.
     template<typename T>
     using VarResult = std::expected<T, VarError>;
 
+    /**
+     * @brief The pair representing an environment variable.
+     * @details The left side is the name of variable. The right side is the content of variable.
+     */
+    using VarPair = std::pair<std::u8string, std::u8string>;
+
     /**
      * @brief Get the value of given environment variable name.
      * @param[in] name The name of environment variable
@@ -61,17 +67,21 @@ namespace yycc::env {
      */
     VarResult<void> del_var(const std::u8string_view& name);
 
+    /**
+     * @brief Returns an list of (variable, value) pairs of strings, 
+     * for all the environment variables of the current process.
+     * @return The list holding all variables.
+     */
+    VarResult<std::vector<VarPair>> get_vars();
+
 #pragma endregion
 
 #pragma region Environment Path
 
     /// @brief Error occurs when operating path related functions.
     enum class PathError {
-        Win32,    ///< Underlying Win32 function error.
-        Posix,    ///< Underlying POSIX failed.
-        BadSize,  ///< Written size if not matched with expected size.
-        BadCast,  ///< Error occurs when casting values.
-        Overflow, ///< Some arithmetic operation overflow.
+        SysCall, ///< Underlying system calling error.
+        Others,  ///< Any other error types.
     };
 
     /// @brief The result type used for path related functions;
@@ -79,10 +89,49 @@ namespace yycc::env {
     using PathResult = std::expected<T, PathError>;
 
     /**
-     * @brief Get the path of the current running executable.
-     * @return Gotten path (no absolute path guaranteed) or error occurs.
+     * @brief Returns the current working directory.
+     * @return Current working directory path or error occurs.
      */
-    PathResult<std::u8string> current_exe();
+    PathResult<std::filesystem::path> current_dir();
+
+    /**
+     * @brief Returns the path of the current running executable.
+     * @return Current running executable path or error occurs.
+     * Please note that there is no guarantee that return path is absolute path.
+     */
+    PathResult<std::filesystem::path> current_exe();
+
+    /**
+     * @brief Returns the path of the current user's home directory if known.
+     * @return Current user's home directory path or error occurs.
+     */
+    PathResult<std::filesystem::path> home_dir();
+
+    /**
+     * @brief Returns the path of a temporary directory.
+     * @return The path of a temporary directory.
+     */
+    PathResult<std::filesystem::path> temp_dir();
+
+#pragma endregion
+
+#pragma region Environment Argument
+
+    /// @brief Error occurs when operating argument related functions.
+    enum class ArgError {
+        SysCall, ///< Underlying system calling error.
+        Others,  ///< Any other error types.
+    };
+
+    /// @brief The result type used for argument related functions;
+    template<typename T>
+    using ArgResult = std::expected<T, ArgError>;
+
+    /**
+     * @brief Returns the arguments that this program was started with (normally passed via the command line).
+     * @return The list holding all argument one by one.
+     */
+    ArgResult<std::vector<std::u8string>> get_args();
 
 #pragma endregion