78 lines
1.8 KiB
JavaScript
78 lines
1.8 KiB
JavaScript
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// @ts-check
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"use strict";
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/**
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* Intern strings or objects, so there is only one copy of each, by value.
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* Objects may need to be converted to another representation before storing.
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* Each inputs corresponds to a number, starting with 0.
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*
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* @template [T=string],[V=T]
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*/
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class Intern {
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/**
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* @typedef {object} InternOptions
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* @property {(input: V) => string} [stringify=String] Represent the
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* converted input as a string, for value comparison.
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* @property {(input: T) => V} [convert=(x) => x] Convert the input to its
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* stored form. Required if type V is not the same as type T. Return
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* falsy value to have this input not be added; add() will return -1 in
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* this case.
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*/
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/**
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* @param {InternOptions} [options]
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*/
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constructor(options) {
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/** @type {Required<InternOptions>} */
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this.options = {
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stringify: String,
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convert: x => /** @type {V} */ (/** @type {unknown} */ (x)),
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...options,
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};
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/** @type {V[]} */
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this.items = [];
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/** @type {Record<string, number>} */
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this.offsets = {};
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}
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/**
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* Intern an item, getting it's asssociated number. Returns -1 for falsy
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* inputs. O(1) with constants tied to the convert and stringify options.
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*
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* @param {T} input
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* @return {number}
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*/
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add(input) {
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const c = this.options.convert(input);
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if (!c) {
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return -1;
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}
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const s = this.options.stringify(c);
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let num = this.offsets[s];
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if (num === undefined) {
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num = this.items.push(c) - 1;
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this.offsets[s] = num;
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}
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return num;
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}
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/**
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* @param {number} i
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* @returns {V}
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*/
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get(i) {
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return this.items[i];
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}
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/**
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* @template U
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* @param {(value: V, index: number, array: V[]) => U} fn
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* @returns {U[]}
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*/
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map(fn) {
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return this.items.map(fn);
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}
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}
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module.exports = Intern;
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