This is more of an addition to your list, but I think adding

the | operator for getting the optional value or a default value would be nice. For example:

optional<double> safe_sqrt(double x) { if (x < 0) return none; else return sqrt(x); }

double x = safe_sqrt(4) | 0; //x = 4 double y = safe_sqrt(-1) | 0; //y = 0 I dont know if this is possible for tr2, but would be really nice addition in the future. Especially, since a lot of times i just want a default value if the optional value doesn't exist.

Note, that boost::optional already provides a functionality for that, although with a slightly more verbose syntax: double x = safe_sqrt(4).get_value_or(0); std::tr2::optional would also provide this functionality. If this is only about shorthand notation, this item would be controversial. bitwise-or is a better choice that logical-or but it might turn out too confusing and disturbing for programmers that do not want to learn what overloaded operators mean for every type they use. What I mean to say is that liberal use of overloaded operators is a general controversy. Regards, &rzej