@tolokoban/tgd
Version:
ToloGameDev library for WebGL2
50 lines • 3.28 kB
JavaScript
/**
* A Reference Map counts how many time you want to insert the same key.
* And it tells you when you delete it as many times.
*/
export default class ReferenceMap {
constructor() {
this.map = new Map();
this.count = new Map();
}
/**
* If `key` is already stored in the map,
* we add a reference to the mapped value and return it.
* If not, we create the mapped value by calling `factory()`.
*/
add(key, factory) {
const { map, count } = this;
if (count.has(key)) {
count.set(key, 1 + (count.get(key) ?? 0));
const currentValue = map.get(key);
if (!currentValue)
throw new Error("[CountMap] Map should not be empty!");
return currentValue;
}
const newValue = factory();
map.set(key, newValue);
count.set(key, 1);
return newValue;
}
/**
* Delete a reference to `key`.
* If the last reference has been removed,
* then return the mapped value, otherwise
* return `undefined`.
*/
delete(key) {
const { map, count } = this;
if (!map.has(key))
return;
const newCount = (count.get(key) ?? 0) - 1;
if (newCount > 0) {
count.set(key, newCount);
return;
}
const value = map.get(key);
map.delete(key);
count.delete(key);
return value;
}
}
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