Hello: I am constantly trying to jump into boost. However, I can only read so many pages of documentation before my brain explodes. I have always been interested in a data structure for storing pairs of of keys. In math it is a one-to-one mapping. I find it useful from time to time to have a container that allows me to treat it like an enum, but then to do the operation the other way. I usually do it lazily and just do a map and then do a linear search for the value when I need to. However, I have been thinking about it, and why should I have to suffer linear half the time? So today I wrote a very ugly class that does it log n both ways for me. I did it in less than 30 minutes so it has three methods, namely, insert, get_by_first and get_by_second. It is exceptionally ugly because you have to guaruntee that you will never change the data structure by returning a reference to one of the keys. Worse, if you want to save memory and make sure comparisons work the way you expect them, you have to use two maps of pointers with custom comparison functions that call the user's comparison function with the key-pointers dereferenced! I am wondering if there is something like this already out there already. Or is there a better way of dealing with my issue? I want structures that let me go on to things like one-to-many and many-to-many as well. Of course, what would "many" look like? Would it be an array of the mapped values? Perhaps I should stick with one-to-one! Finally, what would be a good name for this structure? I have been calling it bi-directional map. But this name doesn't carry well for one-to-many and many-to-many. And what should the interface look like? This structure is kind of hard to map to a STL container's interface due to the two keys (no operator[] for instance and no mapped_type or key_type). Thanks for any input! Ask if you want my horrible source code. Ever see two const_casts in one line? Want to?