npm package: @rbxts/silo
Description: State management
Author: sleitnick
Latest version: 0.2.0

# Silo
State management based on Redux slices.

## Usage

### Create a Silo
Creating a new silo is easy. Define the state and modifiers, and then create the silo via
`createSilo()`, passing along the initial state and the modifier implementations.
```ts
// Define the shape of the state:
interface MyState {
	kills: number;
	points: number;
}

// Define the modifier actions:
interface MyModifiers {
	addKill: (state: MyState) => MyState;
	addPoints: (state: MyState, points: number) => MyState;
}

// Create the Silo:
const mySilo = createSilo<MyState, MyModifiers>(
	{
		// Default state:
		kills: 0,
		points: 0,
	},
	{
		// Modifier implementations:
		addKill: (state) => {
			return {
				...state,
				kills: state.kills + 1,
			};
		},
		addPoints: (state, points) => {
			return {
				...state,
				points: state.points + points,
			};
		},
	},
);
```

### Modifying state via actions
Modifiers can be accessed through the `actions` property of a silo. Actions are functions
that are identical to the modifier implementation, except the first `state` argument is
dropped, since the silo can inject that itself.

For instance, to use the `addKill` and `addPoints` modifiers, we can call the resulting actions
as `mySilo.actions.addKill` and `mySilo.actions.addPoints`:
```ts
// Add kill:
mySilo.actions.addKill();

// Add 15 points:
mySilo.actions.addPoints(15);
```

### Fetching state
Use the `getState()` function to get the current state of a silo.
```ts
print(mySilo.getState());
print(`Points: ${mySilo.getState().points}`);
```

### Listening for state changes
Use the `subscribe` function to subscribe to all future changes to the entire state, which
will also include a copy of the old state.

Use the `observe` function to observe a specific selection of the state, which will then fire
the given observer function anytime the selection changes, including the immediate value.

Observers can optionally be given a `changed` callback, which will control whether or not the
observer is triggered. Any time the silo's state changes, the `changed` callback will be given
the new and old value of the selector, and the callback must return whether or not the value
has changed. This is useful for checking for table value changes or other dynamic changes that
go beyond the default `old !== new` comparison.

```ts
// Subscribe to changes to the state:
mySilo.subscribe((newState, oldState) => {
	print("State changed");
});

// Observe points:
mySilo.observe((state) => state.points, (points) => {
	print(`Points: ${points}`);
});

// Observing state with a specified `changed` callback:
mySilo.observe(
	(state => state.points),
	(points) => print(points),
	// Only trigger observer if points have changed by more than 5:
	(newPoints, oldPoints) => math.abs(newPoints - oldPoints) > 5,
);

// The `subscribe` and `observe` functions return functions that can be called
// in order to stop subscribing/observing:
const unsubscribe = mySilo.subscribe((newState, oldState) => {});
unsubscribe();

const stopObserving = mySilo.observe((state) => state.points, (points) => {});
stopObserving();
```

### Cleanup
If a silo needs to be cleaned up during runtime, call the `destroy()` function on the silo.
All this function does is clear out the subscriber/observer list internally.
```ts
mySilo.destroy();
```

### Combine Silos
It is common to have more than one silo. Use the `combineSilo` function to create a wrapper
silo around multiple silos. The individual silos can still be used, but the combined silo
can be used to help manage and observe state.

```ts
// Assuming we have the `mySilo` from the first example.

interface AnotherState { message: string }
interface AnotherModifiers {
	setMessage: (state: AnotherState, msg) => AnotherState;
}
const anotherSilo = createSilo<AnotherState, AnotherModifiers>(
	{ message: "" },
	{ setMessage: (state, msg) => ({...state, message: msg}) },
);

// Combine `mySilo` and `anotherSilo`:
const silos = combineSilos({
	my: mySilo,
	another: anotherSilo,
});

// Calling `getState()` returns a combined state of all silos:
print(`Message: ${silos.getState().another.message}`);

// Individual silos can also be accessed through the `all` property:
print(`Message: ${silos.all.another.getState().message}`);

// Observe the current message & future changes to the message:
silos.observe((state) => state.another.message, (msg) => {
	print(`Observing message: ${msg}`);
});

// Set a message:
silos.all.another.actions.setMessage("Hello world");
```