Suppose we have a program like this:
void main() {
// Point 0
BigThing bt = new BigThing();
// Point 1
WeakReference<BigThing> weak = new WeakReference<>(bt);
// Point 2
doSomething(weak);
// Point 3
}
void doSomething(...) { ... }
We know that the weak reference to the BigThing object cannot prevent the object from being garbage collected when it becomes no longer strongly reachable.
My question is about the local variable bt which is a strong reference to the BigThing object. Does the object become not-strongly-reachable at point 2 (just before calling doSomething()) or at point 3 (end of block scope)?
The answer to this question will affect whether the call to doSomething() is guaranteed to be able to access the live BigThing object, or whether the underlying object can die during the function call.
I am uncertain because you could argue that after point 2, the local variable bt is never read or written anymore, so the variable is effectively dead and the pointer value can be discarded. This "optimization" would be valid if all references were strong, but the reasoning falls apart when the notions of soft, weak, and phantom references are introduced, and finalizers as well. Also as an analogy, because C++ has destructors, a value must be destructed at the end of the scope, and cannot be moved ahead to the point of last usage.
