Jody Hagins wrote:
I'm the one asking YOU for reasons why immutable interfaces should be used over mutable ones ;-) You are the one making a proposal in favor of immutable interfaces. Aside from being able to represent the functional paradigm in C++, what are the benefits from your point of view? I've read several papers, and I've used several similar libraries, but I want your experience stories because I respect your talent and experience.
Why should the interfaces for string (or other boost libraries) be immutable? I am unaware of an immutable implementation that provides transparent performance cost. I'd be most interested if you know of one.
Because it is desirable to have cheap string copying. The most effective solution is to use reference counted string with copy-on-write. AFAIK, no one has come up with a thread safe implementation for COW std::basic_string, it's interface is too leaky (operator[] returns a bare char&, for example). Although GNU C++ std::basic_string is reference counted and COW they say it is not thread safe in some corner cases. http://groups.google.com/group/comp.lang.c++.moderated/msg/0aa848d97e205d72 Cheap copy is the only motivation behind an immutable string. One implementation has been reported to perform well as a drop-in replacement for std::basic_string. http://article.gmane.org/gmane.comp.lib.boost.devel/110029