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71 lines
3.0 KiB
TypeScript
71 lines
3.0 KiB
TypeScript
// Iterator objects from strings and typed arrays, Iterator.from over the
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// built-in iterables, return() on helper objects, and flatMap over Set,
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// Map and string results.
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const log: string[] = [];
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function* count(label: string, n: number): Generator<number> {
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try {
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for (let i = 1; i <= n; i++) {
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log.push(`${label}${i}`);
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yield i;
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}
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} finally {
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log.push(`${label}:closed`);
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}
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}
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function flush(what: unknown): void {
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console.log(what, "|", log.join(" "));
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log.length = 0;
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}
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// String iterators step by code point; a lone surrogate is one step.
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const text = "a\u{1F600}b\uD800";
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const chars = text[Symbol.iterator]();
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console.log(chars.next(), chars.next().value?.length, [...chars].length);
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console.log(text[Symbol.iterator]().map((c) => c.codePointAt(0)!.toString(16)).toArray());
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console.log("naïve"[Symbol.iterator]().filter((c) => c !== "ï").toArray().join(""));
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for (const c of "xyz"[Symbol.iterator]().drop(1)) console.log("char", c);
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console.log("hello"[Symbol.iterator]().some((c) => c === "l"), "hello"[Symbol.iterator]().find((c) => c > "h"));
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// Typed array iterators.
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const bytes = new Uint8Array([9, 8, 7]);
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console.log(bytes.values().map((x) => x * 2).toArray(), bytes.keys().filter((i) => i > 0).toArray());
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console.log(bytes.entries().map(([i, v]) => i * v).toArray());
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const floats = new Float64Array([0.5, 1.5, 2.5]).values().map((x) => x + 1);
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console.log(floats.next(), [...floats]);
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for (const [i, v] of new Int16Array([-1, 2, -3, 4]).entries().filter(([, v]) => v > 0)) console.log(i, v);
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// Iterator.from returns each built-in iterable's own iterator.
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const list = [1, 2];
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const fromList = Iterator.from(list);
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list.push(3);
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console.log([...fromList], Iterator.from("a\u{1F600}").toArray());
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console.log(Iterator.from(new Set(["p", "q"])).toArray(), Iterator.from(new Map([["k", 1]])).toArray());
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console.log(Iterator.from(new Uint8Array([4, 5])).reduce((a, b) => a + b, 0));
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const fromGen = Iterator.from(count("a", 3));
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flush([fromGen.next(), fromGen.take(1).toArray()]);
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flush(Iterator.from(count("b", 9).map((x) => x * 3)).take(2).toArray());
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// return() on helper objects.
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const started = count("c", 3);
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started.next();
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const doubled = started.map((x) => x * 2);
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flush([doubled.return!(), started.next()]);
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const fresh = count("d", 3);
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const kept = fresh.filter(() => true);
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flush([kept.return?.(), fresh.next(), kept.next()]);
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const stepping = count("e", 5).drop(1);
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flush([stepping.next(), stepping.return!(), stepping.next()]);
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flush(count("f", 4).map((x) => x).take(2).return!());
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// flatMap over Set and Map results, and a string result's TypeError.
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console.log([1, 2].values().flatMap((x) => new Set([x, x * 10])).toArray());
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console.log([1, 2].values().flatMap((x) => new Map([[`k${x}`, x]])).toArray());
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const pairs = new Map<string, number>([["m", 1], ["n", 2]]);
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for (const [k, v] of [0].values().flatMap(() => pairs)) console.log(k, v);
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try {
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count("g", 3).flatMap((x) => `s${x}`).toArray();
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} catch (e) {
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log.push(`${(e as Error).name}: ${(e as Error).message}`);
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}
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flush("string result");
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