Hi to all, While revising a bit the boost::filesystem error/exception use for looking a model for interprocess library and after reading the N1934 "Filesystem Library Proposal for TR2 (Revision 2)" I'm a bit concerned about the heavy use of std::string/string_type in the library. The following functions return some kind of path as value type: // observers const string_type string() const; const string_type file_string() const; const string_type directory_string() const; const external_string_type external_file_string() const; const external_string_type external_directory_string() const; string_type root_name() const; string_type root_directory() const; basic_path root_path() const; basic_path relative_path() const; string_type leaf() const; basic_path branch_path() const; I know that syntactically this is nicer and we can have RVO: string_type str = path.string(); But when iterating through directories I find that that returning a temporary object that must allocate/copy/deallocate hurts my performance paranoia. Even with move semantics we have a an overhead: std::vector<std::path> paths; //fill with paths std::path::iterator beg = paths.begin(), end = paths.end(); for(; beg != end; ++it){ std::path::string_type str = it->root_name();//temporary created str += "append some data"; std::cout << str; } Couldn't be better (although uglier) to take a reference to a string that will be filled? void fill_root_name(string_type &root_name) const; ... //////////////////////////////////////////////////////////////////// std::vector<std::path> paths; //fill with paths std::path::string_type root_name; root_name.reserve(PATH_LENGTH); std::path::iterator beg = paths.begin(), end = paths.end(); for(; beg != end; ++it){ it->fill_root_name(root_name); str += "append some data"; std::cout << str; } This way we only allocate memory if we don't have enough place in our string. We can also reserve it beforehand to speed up code. Apart from this I see that path::iterator has a string member. dereference will return a reference to that member but an iterator is supposed to be a "lightweight" pointer-like abstraction, which is value-copied between functions. A string member, in my opinion, converts an iterator in a heavy class (that depends on the string length, but an small string optimization of 16 bytes is not going to help much). Now that filesystem is proposed for the standard I would like to ask boosters (and Beman, of course) if they find these performance concerns serious enough. Regards, Ion