Added array at method

arr.test.ts

@@ -10,6 +10,7 @@ import { int8 } from './int/8.ts';
 import { pointer } from './ptr.ts';
 import { Struct } from './struct.ts';
 import { getByteLength, getByteOffset } from './util.ts';
+import { Uint8Ptr } from './mod.ts';
 
 class Foo extends Struct {
 	declare public bar: number;
@@ -98,6 +99,24 @@ Deno.test('array: Symbol.iterator', () => {
 	}
 });
 
+Deno.test('array: at', () => {
+	const jsar = [1, 2, 3, 4];
+	const data = new Uint8Array(jsar);
+	const Four = array(Uint8Ptr, 4);
+	const four = new Four(data.buffer);
+
+	for (
+		const index of [
+			[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
+			[-1, -2, -3, -4, -5, -6, -7, -8, -9, -10],
+			[Infinity, -Infinity, NaN, Number.EPSILON, -Number.EPSILON],
+			[1.1, 0.5, -1.1, -0.5, -0],
+		].flat()
+	) {
+		assertStrictEquals(four.at(index), jsar.at(index), `at(${index})`);
+	}
+});
+
 Deno.test('array: extend', () => {
 	// Weird but not invalid.
 	class FooExtra extends Foo4 {

arr.ts

@@ -23,6 +23,13 @@ export interface Arr<T = never> extends Ptr<T>, Type {
 	 */
 	readonly length: number;
 
+	/**
+	 * Get value at index.
+	 *
+	 * @param i Index, can be negative.
+	 */
+	at(i: number): T | undefined;
+
 	/**
 	 * Array iterator.
 	 */
@@ -135,6 +142,14 @@ export function array<T extends Type>(
 						return length;
 					}
 
+					public at(i: number): T | undefined {
+						i ||= 0;
+						i -= i % 1;
+						if ((i < 0 ? i += length : 0) >= 0 && i < length) {
+							return this[i];
+						}
+					}
+
 					public static readonly BYTE_LENGTH = (
 						Ptr.BYTES_PER_ELEMENT * length
 					);