this is a good question :)
But so far there is nothing special for that
you can define a method on the trait
and invoke it via new when you create an object
Now this is not really cool because
T1>>initialize
foo := 3
T2>>initialize
bar := 4
C = T1 + T2
=> conflicts
so we should use alias and this is not really what we want
C>>initialize
self T2initialize
self T3initialize
Note that stateful traits is more experimental than stateless one.