[Uploaded to the vault (flags_v1.zip) – complete with docs and test file (no jam file yet – sorry) - tested in vc8 and MinGW GCC 3.4.2.] I’ve proposed this before and gotten a little interest – so I figured I’d try again (particularly now that 1.34.1 is out) and see if I could get some more interest! At its most simple, it’s a way to stop function users providing difficult to detect erroneous data. The best way to work out what this lib does is probably read the docs I uploaded, but for here I’ll take one of the examples I use from the docs: using boost::flags enum foo { foo_1 = 1<<0, foo_2 = 1<<1, }; enum bar { bar_1 = 1<<2, bar_2 = 1<<3, }; void func1(unsigned int options) { //do stuff } void func2(flags<foo> options) { //do stuff } int main(int argc, char * argv[]) { func1(foo_1 | foo_2 | bar_1 | bar_2); //Compiles fine func2(flags<foo>(foo_1) | foo_2 | bar_1 | bar_2); //Compile time error - cannot convert bar to foo } Additionally, sometimes it is useful to force the user to supply a flag rather than allow them to supply none (i.e. '0') - the flags_no_default provides this functionality. The library is not very big and it’s not very clever :) but the hope is to push errors back to compile time, at little or no runtime cost. If people are interested or not either way it’s cool – but since it’s now in the vault anyone can use it if they want. Hope it all makes sense! Questions/comments/criticism gratefully received. IAIN