David Abrahams wrote:
on Tue Sep 08 2009, Vicente Botet Escriba <vicente.botet-AT-wanadoo.fr> wrote:
Do you have a specific pointer for CLang related to this usage?
Nope, this is hearsay. Doug?
If I remember Doug's explanation correctly, one of the optimizations inside clang is: There is a global table of 'plain' types, e.g. int, bool, float, std::string. Clang internally represents CV qualified types by e.g. creating a pointer to the type 'int', then using the small bits of the pointer to tag const and volatile. I don't recall whether they used more than two bits (for, say reference, static, pointer, etc.) Sebastian Redl gave a great intro to clang @ boostcon, I'd bet he knows the details as well. Aside from that, another use case: Mark-and-sweep garbage collection. This came up when as an exercise I implemented a lisp interpreter with spirit, variants, visitors, and intrusive_ptr. Currently this thing just leaks pointer loops, and a taggable_ptr combined with some kind of memory pool would seem a nice way to start working on it... -t