Do not use protected data members

include/tmp/path.hpp

@@ -12,6 +12,8 @@ namespace tmp {
 /// Subclass this and provide mktemp-like function to the constructor to create
 /// temporary files and directories.
 class path {
+    std::filesystem::path underlying;    ///< This path
+
 public:
     /// Returns the underlying path
     operator const std::filesystem::path&() const noexcept;
@@ -28,8 +30,6 @@ class path {
     auto operator=(const path&) = delete;    ///< not copy-assignable
 
 protected:
-    std::filesystem::path underlying;    ///< This file path
-
     /// Creates a unique temporary path using the given constructor function.
     /// @param prefix the path between system temp
     /// @param creator wrapped mktemp-like function that returns resulting path

lib/file.cpp

@@ -43,8 +43,8 @@ std::filesystem::path file::create(std::string_view prefix) {
 std::ofstream file::stream(bool append) const noexcept {
     std::ios::openmode mode = append ? std::ios::app : std::ios::trunc;
     return this->binary
-           ? std::ofstream { this->underlying, mode | std::ios::binary }
-           : std::ofstream { this->underlying, mode };
+           ? std::ofstream { static_cast<const std::filesystem::path&>(*this), mode | std::ios::binary }
+           : std::ofstream { static_cast<const std::filesystem::path&>(*this), mode };
 };
 
 }    // namespace tmp