LazyMap class

[aleclarson]

Leaving this here so I don't lose it. Upvote if you think it belongs in Radashi. While historically we haven't embraced classes, there are times when they can be appropriate, especially since Radashi wants to align with JavaScript's standard library when there already exists similar concepts (for API familiarity).

class LazyMap<K, V> extends Map<K, V> {
  constructor(
    private compute: (key: K, map: LazyMap<K, V>) => V,
    private onCompute?: (key: K, value: V, map: LazyMap<K, V>) => void,
  ) {
    super()
  }

  get(key: K): V | undefined {
    if (!super.has(key)) {
      const value = this.compute(key, this)
      super.set(key, value)
      this.onCompute?.(key, value, this)
    }
    return super.get(key)
  }
}