I have a newbie kind of question which I cant get my head around. How does the Proc in the if condition of the caches_action get executed for the caches_action method.

for example caches_action :show, :if=>Proc.new{|x| something} what i dont get its how does this get called. I know i can execute a proc defined as

proc= Proc.new by proc.call

so i dont understand how this gets called. Second how do I pass conditions like

if logged_in?

I'd appreciate any help on this