/**
* Creates an array that can have negative indexes using a JavaScript Proxy.
*
* @example
* ```ts
* const array = new NegativeArray(1, 2, 3, 4, 5);
* console.log(array[-1]); // Output: 5
* array[-2] = 42;
* console.log(array[3]); // Output: 42
* console.log(array[10]); // Output: undefined
* ```;
*
* @param arrayToProxy - The array to be proxied.
* @returns A proxied array allowing negative indexing.
* @see A. Balane, "JavaScript array negative index using proxies," Medium,
* https://medium.com/uncaught-exception/javascript-array-negative-index-using-proxies-ed096dc84416
*/
export class NegativeArray<T> extends Array<T> {
constructor(...items: T[]) {
super(...items);
// eslint-disable-next-line no-constructor-return
return new Proxy(this, {
get(
target: T[],
property: string | symbol,
receiver: any,
): T | undefined {
if (typeof property === "string" && !Number.isNaN(Number(property))) {
let propertyValue = Number.parseInt(property, 10);
if (propertyValue < 0) propertyValue += target.length;
return target[propertyValue];
}
// Safe casting of the Reflect.get return value to expected type
return Reflect.get(target, property, receiver) as T | undefined;
},
set(
target: T[],
property: string | symbol,
value: T,
receiver: any,
): boolean {
if (typeof property === "string" && !Number.isNaN(Number(property))) {
let propertyValue = Number.parseInt(property, 10);
if (propertyValue < 0) propertyValue += target.length;
target[propertyValue] = value; // Safe assignment of typed value
return true;
}
return Reflect.set(target, property, value, receiver);
},
});
}
}
import {NegativeArray} from "../../../../data/algorithms/src/util/negative_array.ts";
import {assertEquals} from "$assert";
test(function testNegativeIndices() {
const narr = new NegativeArray<number>(1, 2, 3, 4);
assertEquals(narr[-1], 4);
assertEquals(narr[-2], 3);
assertEquals(narr[-3], 2);
assertEquals(narr[-4], 1);
});
test(function testNegativeOutOfRange() {
const narr = new NegativeArray<number>(1, 2, 3, 4);
assertEquals(narr[-5], undefined);
assertEquals(narr[-6], undefined);
});
test(function testSetNegative() {
const narr = new NegativeArray<number>(1, 2, 3, 4);
narr[-1] = 9;
assertEquals(narr[3], 9);
narr[-4] = 0;
assertEquals(narr[0], 0);
});
test(function testNominalArray() {
const narr = new NegativeArray<number>(1, 2, 3, 4);
assertEquals(narr[0], 1);
assertEquals(narr[1], 2);
assertEquals(narr[2], 3);
assertEquals(narr[3], 4);
narr[0] = 9;
assertEquals(narr[0], 9);
narr[3] = 8;
assertEquals(narr[3], 8);
});