Consider the chance of that resource can be shared when cleaning up

[takahirox]

Cleaning up system code is like

const fooExitQuery = exitQuery(defineQuery([FooComponent]));

export const fooSystem = (world: IWorld): void => {
  fooExitQuery(world).forEach(eid => {
    const proxy = FooProxy.get(eid);
    const foo = proxy.foo;
    foo.close();
    proxy.free();
  });     
};

Consider the change of that resource can be shared. For example, foo.close() should be called only if it isn't referenced from somewhere else. We may need reference count?

[takahirox]

An idea

// utils/reference.ts
const referenceCounts: Map<Object, number> = new Map();

export const referenceCountUp = (obj: Object): number => {
  if (!referenceCounts.has(obj)) {
    referenceCounts.set(obj, 0);
  }
  const newCount = referenceCounts.get(obj)! + 1;
  referenceCounts.set(obj, newCount);
  return newCount;
};

export const referenceCountDown = (obj: Object): number => {
  const newCount = referenceCounts.get(obj)! - 1;
  if (newCount === 0) {
    referenceCounts.delete(obj);
  } else {
    referenceCounts.set(obj, newCount);
  }
  return newCount;
};

// Somewhere for creation
import { referenceCountUp } from "utils/reference";

const foo = new Foo();
addComponent(world, FooComponent, eid);
FooProxy.get(eid).allocate(foo);
referenceCountUp(foo);

// Somewhere for deletion
import { referenceCountDown } from "utils/reference";

const proxy = FooProxy.get(eid);
const foo = proxy.foo;
if (referenceCountDown(foo) === 0) {
  foo.close();
}
proxy.free();
removeComponent(world, Foo, eid);