Philippe Vaucher wrote:
How do you make a std::set of structs, pairs, or tuples?
Maybe it was already said (didn't read the whole thread), but I thought I'd add my 0.02$.
I think we should not define meaningless operator< for the structs/whatever, and let the user define one if he wants to use those structs in a set.
That's the claim being made in this thread, true. The user can't necessarily define operator< for a foreign class because different users may have different ideas about what operator< should do, so their translation units won't be able to coexist. It is the responsibility of the author of the class to define its operator< (if there is one.) This leaves us with the option of defining and using custom comparators. So, if the author of pair<> does nothing, every time you need to make a set out of pair<X, Y>, you'll need to define a separate function object for it. This isn't very convenient; most of these function objects would end up being exact copies. So maybe the author of pair<> needs to provide a comparator. template<class P> struct pair_compare { bool operator()( P const & p ) const { // ??? } }; What would you put in the ??? portion? (Warning, this is a trap.)