I would like to run some code when something is
garbage-collected. Fine, he says, just the job for
finalizers (module Weak). Unfortunately, they don't
seem to offer a general solution, as the code below
demonstrates (presumably, smallish things are copied,
not shared, so that the finalizers run too early?).
Is there a general way to add finalizers to values
of arbitrary type (and have them run when the value,
not just one copy of it, disappears)? Or is this
behaviour -he hopes- a bug, to be fixed in the next
release?
Claus
------------- session
Main> y
nothing is
0
Main> x
nothings are
(0,0)
Main> runAllFinalizers
nothing was
Main> y
0
Main> x
(0,0)
------------- program
import IOExts
import Weak
y = unsafePerformIO $
do { x<-return 0
; putStrLn "nothing is"
; addFinalizer x (putStrLn "nothing was")
; return x
}
x = unsafePerformIO $
do { x<-return (0,0)
; putStrLn "nothings are"
; addFinalizer x (putStrLn "nothings were")
; return x
}
