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Merge pull request #92 from mcpower/from-string-cache
Add cache for fromString
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,139 @@ | ||
| /** | ||
| * A LRU cache intended for caching pure functions. | ||
| */ | ||
| export class LRUCache<K, V> { | ||
| private map = new Map<K, ListNode<K, V>>(); | ||
| // Invariant: Exactly one of the below is true before and after calling a | ||
| // LRUCache method: | ||
| // - first and last are both undefined, and map.size() is 0. | ||
| // - first and last are the same object, and map.size() is 1. | ||
| // - first and last are different objects, and map.size() is greater than 1. | ||
| private first: ListNode<K, V> | undefined = undefined; | ||
| private last: ListNode<K, V> | undefined = undefined; | ||
| maxSize: number; | ||
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| /** | ||
| * @param maxSize The maximum size for this cache. We recommend setting this | ||
| * to be one less than a power of 2, as most hashtables - including V8's | ||
| * Object hashtable (https://crsrc.org/c/v8/src/objects/ordered-hash-table.cc) | ||
| * - uses powers of two for hashtable sizes. It can't exactly be a power of | ||
| * two, as a .set() call could temporarily set the size of the map to be | ||
| * maxSize + 1. | ||
| */ | ||
| constructor(maxSize: number) { | ||
| this.maxSize = maxSize; | ||
| } | ||
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|
||
| get size(): number { | ||
| return this.map.size; | ||
| } | ||
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| /** | ||
| * Gets the specified key from the cache, or undefined if it is not in the | ||
| * cache. | ||
| * @param key The key to get. | ||
| * @returns The cached value, or undefined if key is not in the cache. | ||
| */ | ||
| get(key: K): V | undefined { | ||
| const node = this.map.get(key); | ||
| if (node === undefined) { | ||
| return undefined; | ||
| } | ||
| // It is guaranteed that there is at least one item in the cache. | ||
| // Therefore, first and last are guaranteed to be a ListNode... | ||
| // but if there is only one item, they might be the same. | ||
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| // Update the order of the list to make this node the first node in the | ||
| // list. | ||
| // This isn't needed if this node is already the first node in the list. | ||
| if (node !== this.first) { | ||
| // As this node is DIFFERENT from the first node, it is guaranteed that | ||
| // there are at least two items in the cache. | ||
| // However, this node could possibly be the last item. | ||
| if (node === this.last) { | ||
| // This node IS the last node. | ||
| this.last = node.prev; | ||
| // From the invariants, there must be at least two items in the cache, | ||
| // so node - which is the original "last node" - must have a defined | ||
| // previous node. Therefore, this.last - set above - must be defined | ||
| // here. | ||
| // eslint-disable-next-line @typescript-eslint/no-non-null-assertion | ||
| this.last!.next = undefined; | ||
| } else { | ||
| // This node is somewhere in the middle of the list, so there must be at | ||
| // least THREE items in the list, and this node's prev and next must be | ||
| // defined here. | ||
| // eslint-disable-next-line @typescript-eslint/no-non-null-assertion | ||
| node.prev!.next = node.next; | ||
| // eslint-disable-next-line @typescript-eslint/no-non-null-assertion | ||
| node.next!.prev = node.prev; | ||
| } | ||
| node.next = this.first; | ||
| // From the invariants, there must be at least two items in the cache, so | ||
| // this.first must be a valid ListNode. | ||
| // eslint-disable-next-line @typescript-eslint/no-non-null-assertion | ||
| this.first!.prev = node; | ||
| this.first = node; | ||
| } | ||
| return node.value; | ||
| } | ||
|
|
||
| /** | ||
| * Sets an entry in the cache. | ||
| * | ||
| * @param key The key of the entry. | ||
| * @param value The value of the entry. | ||
| * @throws Error, if the map already contains the key. | ||
| */ | ||
| set(key: K, value: V): void { | ||
| // Ensure that this.maxSize >= 1. | ||
| if (this.maxSize < 1) { | ||
| return; | ||
| } | ||
| if (this.map.has(key)) { | ||
| throw new Error("Cannot update existing keys in the cache"); | ||
| } | ||
| const node = new ListNode(key, value); | ||
| // Move node to the front of the list. | ||
| if (this.first === undefined) { | ||
| // If the first is undefined, the last is undefined too. | ||
| // Therefore, this cache has no items in it. | ||
| this.first = node; | ||
| this.last = node; | ||
| } else { | ||
| // This cache has at least one item in it. | ||
| node.next = this.first; | ||
| this.first.prev = node; | ||
| this.first = node; | ||
| } | ||
| this.map.set(key, node); | ||
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||
| while (this.map.size > this.maxSize) { | ||
| // We are guaranteed that this.maxSize >= 1, | ||
| // so this.map.size is guaranteed to be >= 2, | ||
| // so this.first and this.last must be different valid ListNodes, | ||
| // and this.last.prev must also be a valid ListNode (possibly this.first). | ||
| // eslint-disable-next-line @typescript-eslint/no-non-null-assertion | ||
| const last = this.last!; | ||
| this.map.delete(last.key); | ||
| this.last = last.prev; | ||
| // eslint-disable-next-line @typescript-eslint/no-non-null-assertion | ||
| this.last!.next = undefined; | ||
| } | ||
| } | ||
| } | ||
|
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| /** | ||
| * A node in a doubly linked list. | ||
| */ | ||
| class ListNode<K, V> { | ||
| key: K; | ||
| value: V; | ||
| next: ListNode<K, V> | undefined = undefined; | ||
| prev: ListNode<K, V> | undefined = undefined; | ||
|
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| constructor(key: K, value: V) { | ||
| this.key = key; | ||
| this.value = value; | ||
| } | ||
| } |