in reply to conditional enable use bytes for a whole module at compiletime?

I think you can say

BEGIN { package Y; $VERSION = 0.1; 1; package X; if ( $Y::VERSION < 1 ) { # How to enable use bytes for the whole modue X? # with condition $Y::VERSION in mind? ## Not use()'d anymore. # use bytes; require bytes; }

And this will do what you mean.

Note: this is untested code, as always.