Groovy object tracking for binding - binding

Question

I'm developing a Groovy library providing variable binding/syncronization with simple syntax and rich event handler.
Firstly I'm aiming to archive running the following:
def a = 1
def b = 1
def c = 1
a bind { b + c }
assert a==2 & b==1 & c==1
b = 3
assert a==4 & b==3 & c==1
c = -1
assert a==2 & b==3 & c==-1
I'd like avoid Java FX approach of providing additional classes but rather enhance objects with this functionality.
I'm stuck at finding some tracking of objects. Groovy doesn't feature overload of assignment expression.
Currently I see solution in heavy AST transformation (maybe dsld might help).
Maybe there is some object tracking, events or whatever, I've missed?

Answer 1

I'm presuming you are writing your code using scripts. Did what you wanted with the following ideas:
Instead of binding values to keys using the Script.binding, it is better if you create a Variable class which represents both the value and the variable name;
Every method called on the Variable object gets delegated to its value;
A Listener class which encapsulates a reference to the updating operation AND the Variable object which needs to be updated;
An updateListeners() method, to, well, update the listeners;
A bind(closure) method that just bypasses the closure to the variable object. It could pretty much be dropped and written as a { b + c };
class Listener { Closure operation; Variable variable }
class Variable implements GroovyInterceptable {
String name; def value
def invokeMethod(String method, args) {
def var = args[0]
var.class == Variable ?
value."$method"(var.value) : value."$method"(var)
}
}
Variable.metaClass.call = { Closure operation ->
binding['listeners'] <<
new Listener(operation: operation, variable: delegate)
updateListeners()
}
def bind(Closure operation) { operation }
def updateListeners() {
binding.listeners.each {
it.variable.value = it.operation()
}
}
void setProperty(String prop, value) {
if (!binding.hasVariable('listeners')) binding['listeners'] = []
binding[prop] = new Variable(name: prop, value: value)
updateListeners()
}
And your tests worked like a charm.