[Boost-users] typesafe typedef that is not implicitly convertible

I am unable to find it now, but I thought I saw that there is a boost way to define a typedef using a unique class that cannot be implicitly converted to another type. Thus, typedef int Foo; void bar( Foo a ); would compile only with bar( Foo(3) ) not bar(3) Is this capability in Boost 1.33 or am I hallucinating? Thanks, Phil