[Boost-users] [Range] Predicate type checking.

I'm pretty sure I'm have a 'Doh!' moment here, but why does this compile? Surely the last line of main is gibberish; the value type of m is pair, not S, so int_from_S is not a valid function? #include <boost/range.hpp> #include <boost/range/adaptor/transformed.hpp> #include <map> struct S { S( ) { } int i; }; int int_from_S( S s ) { return s.i; } int main( ) { std::map<unsigned, S> m; m[0]=S(); m | boost::adaptors::transformed(int_from_S); } Thx, - Rob.