Re: [boost] Interest in super string class?

From: Maxim Yegorushkin (maxim.yegorushkin_at_[hidden])
Date: 2006-07-07 03:28:50

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