respect const

include/vfs/directory_entry.hpp

@@ -17,16 +17,16 @@ class directory_entry {
 	directory_entry(directory_entry&&) noexcept = default;
 
 	directory_entry(Fs const& fs) noexcept
-	    : fs_(fs.current_path(fs.current_path())) { }
+	    : fs_(fs.shared_from_this()) { }
 
 	explicit directory_entry(Fs const& fs, std::filesystem::path p)
-	    : fs_(fs.current_path(fs.current_path()))
+	    : fs_(fs.shared_from_this())
 	    , path_(std::move(p)) {
 		this->refresh();
 	}
 
 	directory_entry(Fs const& fs, std::filesystem::path p, std::error_code& ec)
-	    : fs_(fs.current_path(fs.current_path()))
+	    : fs_(fs.shared_from_this())
 	    , path_(std::move(p)) {
 		this->refresh(ec);
 	}
@@ -415,7 +415,7 @@ class directory_entry {
 		return this->status().type();
 	}
 
-	std::shared_ptr<Fs>        fs_;
+	std::shared_ptr<Fs const>  fs_;
 	std::filesystem::path      path_;
 	std::filesystem::file_type type_ = std::filesystem::file_type::none;
 };

include/vfs/fs.hpp

@@ -14,7 +14,7 @@ class directory_entry;
 class directory_iterator;
 class recursive_directory_iterator;
 
-class Fs {
+class Fs: public std::enable_shared_from_this<Fs> {
    public:
 	virtual ~Fs() = default;
 
@@ -481,7 +481,7 @@ class Fs {
 	 * @param[in] p Path to change the current working directory to.
 	 * @return Same file system where the working directory is \p p.
 	 */
-	[[nodiscard]] virtual std::shared_ptr<Fs> current_path(std::filesystem::path const& p) const = 0;
+	[[nodiscard]] virtual std::shared_ptr<Fs const> current_path(std::filesystem::path const& p) const = 0;
 
 	/**
 	 * @brief Creates a new Fs that share the same file system but have different working directory.
@@ -490,7 +490,24 @@ class Fs {
 	 * @param[out] ec Error code to store error status to.
 	 * @return Same file system where the working directory is \p p.
 	 */
-	[[nodiscard]] virtual std::shared_ptr<Fs> current_path(std::filesystem::path const& p, std::error_code& ec) const noexcept = 0;
+	[[nodiscard]] virtual std::shared_ptr<Fs const> current_path(std::filesystem::path const& p, std::error_code& ec) const noexcept = 0;
+
+	/**
+	 * @brief Creates a new Fs that share the same file system but have different working directory.
+	 * 
+	 * @param[in] p Path to change the current working directory to.
+	 * @return Same file system where the working directory is \p p.
+	 */
+	[[nodiscard]] virtual std::shared_ptr<Fs> current_path(std::filesystem::path const& p) = 0;
+
+	/**
+	 * @brief Creates a new Fs that share the same file system but have different working directory.
+	 * 
+	 * @param[in]  p  Path to change the current working directory to.
+	 * @param[out] ec Error code to store error status to.
+	 * @return Same file system where the working directory is \p p.
+	 */
+	[[nodiscard]] virtual std::shared_ptr<Fs> current_path(std::filesystem::path const& p, std::error_code& ec) noexcept = 0;
 
 	/**
 	 * @brief Checks whether the path refers to an existing file system object
@@ -1154,4 +1171,6 @@ std::shared_ptr<Fs> make_mem_fs(std::filesystem::path const& temp_dir = "/tmp");
 
 std::shared_ptr<Fs> make_union_fs(Fs& upper, Fs const& lower);
 
+std::shared_ptr<Fs> make_read_only_fs(Fs const& fs);
+
 }  // namespace vfs

internal/vfs/impl/fs.hpp

@@ -1,8 +1,10 @@
 #pragma once
 
+#include <concepts>
 #include <filesystem>
 #include <memory>
 #include <stdexcept>
+#include <type_traits>
 
 #include "vfs/impl/file.hpp"
 
@@ -34,32 +36,20 @@ std::logic_error err_unknown_fs_() {
 
 }  // namespace
 
-inline FsBase& fs_base(Fs& fs) {
-	auto* b = dynamic_cast<FsBase*>(&fs);
+template<typename T>
+requires std::same_as<std::remove_const_t<T>, Fs>
+inline auto& fs_base(T& fs) {
+	auto* b = dynamic_cast<std::conditional_t<std::is_const_v<T>, FsBase const, FsBase>*>(&fs);
 	if(b == nullptr) {
 		throw err_unknown_fs_();
 	}
 	return *b;
 }
 
-inline FsBase const& fs_base(Fs const& fs) {
-	auto const* b = dynamic_cast<FsBase const*>(&fs);
-	if(b == nullptr) {
-		throw err_unknown_fs_();
-	}
-	return *b;
-}
-
-inline std::shared_ptr<FsBase> fs_base(std::shared_ptr<Fs>&& fs) {
-	auto b = std::dynamic_pointer_cast<FsBase>(std::move(fs));
-	if(!b) {
-		throw err_unknown_fs_();
-	}
-	return b;
-}
-
-inline std::shared_ptr<FsBase> fs_base(std::shared_ptr<Fs> const& fs) {
-	auto b = std::dynamic_pointer_cast<FsBase>(fs);
+template<typename T>
+requires std::same_as<std::remove_const_t<T>, Fs>
+inline auto fs_base(std::shared_ptr<T> fs) {
+	auto b = std::dynamic_pointer_cast<std::conditional_t<std::is_const_v<T>, FsBase const, FsBase>>(std::move(fs));
 	if(!b) {
 		throw err_unknown_fs_();
 	}