Stack (Disjoint Union)

The stack operation creates a state that iterates through each parent state sequentially — a disjoint union. Only one parent is active at a time.

from statetracker import Manager, State, stack

with Manager():
    A = State(num_values=2, name="A")
    B = State(num_values=3, name="B")

    C = stack([A, B])  # 5 values (2 + 3)

    for value in C:
        print(f"C={value}, A={A.value}, B={B.value}")

C=0, A=0, B=None
C=1, A=1, B=None
C=2, A=None, B=0
C=3, A=None, B=1
C=4, A=None, B=2

Notice that when A is active, B is None (inactive), and vice versa.

Because stack only activates one parent at a time, it does not cause ConflictingValueAssignmentError even when the stacked states share a common ancestor.