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/**
* LRU Map implementation storing key/values up to a provided size limit. Beyond that
* size limit, the least recently used entry is evicted.
*
* @see https://github.pie.apple.com/isao/lru-map
*/
export class LruMap<K, V> extends Map<K, V> {
private sizeLimit: number;
constructor(sizeLimit: number) {
super();
this.setSizeLimit(sizeLimit);
// Needed to convince TS that this is set (it's actually handled by setSizeLimit)
this.sizeLimit = sizeLimit;
}
/**
* Retrieve a value from the map with a given key.
* @param key The key for the entry
* @return value The entry's value (or undefined if non existent)
*/
get(key: K): V | undefined {
let value: V | undefined;
if (this.has(key)) {
value = super.get(key);
// Map entries are always in insertion order. So
// readding, pushes this entry to the top of the LRU.
this.delete(key);
super.set(key, value!);
}
return value;
}
set(key: K, value: V): this {
super.set(key, value);
this.prune();
return this;
}
setSizeLimit(newSizeLimit: number): void {
if (newSizeLimit < 0 || !isFinite(newSizeLimit)) {
throw new Error(
`setSizeLimit expects finite positive number, got: ${newSizeLimit}`,
);
}
this.sizeLimit = newSizeLimit;
this.prune();
}
private prune(): void {
while (this.size > this.sizeLimit) {
const leastRecentlyUsedKey = this.keys().next().value;
this.delete(leastRecentlyUsedKey);
}
}
}
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