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Compartments

Within NGC-Sim-Lib, the global state serves as the backbone of any given model. This global state is essentially the culmination of all of the dynamic or changing parts of the model itself. Each value that builds this state is stored within a special "container" that helps track these changes over time -- this is referred to as a Compartment.

Practical Information

Practically, when working with compartments, there are a few simple things to keep in mind despite the fact that most of NGC-Sim-Lib's primary operation is behind-the-scenes bookkeeping. The two main points to note are:

  1. Each compartment holds a value and, thus, setting a compartment with myCompartment = newValue will not function as intended since this will overwrite the Python object, i.e., the compartment with newValue. Instead, it is important to make use of the .set() method to update the value stored inside a compartment so myCompartment = newValue becomes myCompartment.set(newValue).
  2. In order to retrieve a value from a compartment, use myCompartment.get(). These methods of getting and setting data inside a compartment are important to use when both working with and designing a multi-compartment component (i.e., Component).

Technical Information

The follow sections are devoted to explication of more technical information regarding how a compartment functions with in the broader scope of NGC-Sim-Lib and, furthermore, to explain how to leverage this information.

How Data is Stored (Within a Model Context)

The data stored inside of a compartment is not actually physically stored within a compartment. Instead, it is stored inside of the global state and each compartment effectively holds the path or key to the right spot in the global state, allowing it to pull out a specific piece of information. As such, it is technically possible to manipulate the value of a compartment without actually touching the compartment object itself within any given component. By default, compartments have in-built safeguards in order to prevent this from happening accidentally; however, directly addressing the compartment within the global state directly has no such safeguards.

What is "Targeting"?

As discussed in the model building section, there is notion of "wiring" together different compartments of different components -- this is at the core of NGC-Learn's and NGC-Sim-Lib's "nodes-and-cables system". These wires are created through the concept of "targeting,", which is, in essence, just the updating of the path stored within a compartment using the path of a different compartment. This means that, if the targeted compartment goes to retrieve the value stored within it, it will actually retrieve the value of a different compartment (as dictated by the target). When a compartment is in this state -- where it is targeting another compartment -- it is set to read-only, which only means that it cannot modify a different compartment.