A while back I've been toying with a combination of macros and templates
that would allow you to write:

vector<int> v;
...
if (5 BELONGS_TO v) { ... }

The idea was to define BELONGS_TO like this:

#define BELONGS_TO *belongs_to*

and then define belongs_to as a global object with the appropriate *
operators.

The scaffolding is quite interesting, but overall I find the idea too whacky
to be acceptable. I kept it on hold just in case I'll run out of ideas for
my Generic<Programming> column, and hopefully I'll never need to use it :o).

Andrei