I couldn't find a good description on the details of how closures capture their
context at http://groovy-lang.org/closures.html. I thought that closures always
capture a reference (and not a snapshot as in Java anonymous classes), because
this works to print 2:
def i = 1
def x = { println i }
i = 2
x()
However, I'm having a problem getting a more complicated example to work. In
this case it's a DSL where I capture a bunch of closures and run them multiple
times, and expecting them to have state.
Here is the DSL "script"
def x = {
def y = func()
println "top closure: y is $y"
setClosure {
println "nested closure: y is $y"
}
}
And here is the "framework"
class State {
def y
Closure closure
def func() {y}
void setClosure(Closure c) {
if (closure == null) {
println "First time and I'm saving the closure"
closure = c
}
}
}
def s = new State()
s.y = 1
x.delegate = s
x()
//s.with(x)
s.closure()
s.y = 2
x()
//s.with(x)
s.closure()
I know that the with method clones the closure, which is why I tried setting
delegate manually. In either case the output is the same:
top closure: y is 1
First time and I'm saving the closure
nested closure: y is 1
top closure: y is 2
nested closure: y is 1
I'm expecting the nested closure to output "y is 2" because on the second
execution of the same closure, y gets set to 2. It seems the nested closure is
capturing a snapshot of the local variable y instead of a reference. If I move
the declaration of "y" out of the top closure, or somewhere else such as a
field in a containing class, it works as expected.
Jason Winnebeck
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