From 3b1afa3ba6fda7f09fe5c4f32056f418ad05410b Mon Sep 17 00:00:00 2001
From: John Maddock
The class compressed pair is very similar to std::pair, but if either of the template arguments are empty classes, then the -"empty member optimisation" is applied to compress the -size of the pair.
+"empty base-class optimisation" is applied to compress +the size of the pair.template <class T1, class T2> class compressed_pair