mirror of
https://github.com/vercel-labs/scriptc.git
synced 2026-10-28 06:53:42 +08:00
Chris Tate
8bb3fa1077
`value.valueOf()` on a dynamic receiver was refused at compile time, a class's own toString was not reached by `value.toString()`, and classes could not declare a `[Symbol.toPrimitive]` method. - `value.valueOf()` lowers to dyn.valueOf, which answers each kind's own valueOf: a primitive itself, a Date its time value, an object with a valueOf member that member's result, and any other object itself. A null-prototype dictionary throws "<spelling> is not a function", and null and undefined throw Node's property-read TypeError. - When a boxed class declares valueOf or toString, `value.valueOf()` and `value.toString(argument)` call the class's method for its instances and keep the runtime call for every other value. - Classes can declare `[Symbol.toPrimitive](hint)`. The dynamic conversions call it with "default" for `+` and `==`, "number" for the numeric operators and conversions, and "string" for template literals, String() and property keys, and throw Node's TypeError when it returns an object.
124 lines
3.3 KiB
TypeScript
124 lines
3.3 KiB
TypeScript
// valueOf() and toString() called on values held as `any`, and classes with
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// a Symbol.toPrimitive method in dynamic conversions. A class's own methods
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// run on the instance itself; primitives, arrays and plain objects answer
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// their own valueOf; Symbol.toPrimitive receives the conversion's hint and
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// must return a primitive.
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const log: string[] = [];
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class Counter {
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total = 0;
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valueOf(): number {
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log.push("valueOf");
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return ++this.total;
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}
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toString(): string {
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log.push("toString");
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return `Counter(${this.total})`;
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}
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}
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class Radix {
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value: number;
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constructor(value: number) {
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this.value = value;
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}
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toString(base?: number): string {
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return base === undefined ? `Radix(${this.value})` : this.value.toString(base);
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}
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}
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class Temperature {
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degrees: number;
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constructor(degrees: number) {
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this.degrees = degrees;
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}
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[Symbol.toPrimitive](hint: string): string | number {
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log.push(`toPrimitive ${hint}`);
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return hint === "string" ? `${this.degrees}°` : this.degrees;
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}
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}
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class Celsius extends Temperature {
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valueOf(): number {
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log.push("Celsius.valueOf");
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return -1;
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}
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}
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class Broken {
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[Symbol.toPrimitive](): object {
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return {};
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}
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}
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class Plain {
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x = 1;
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}
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function show(label: string, value: unknown): void {
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console.log(label, typeof value, value, log.splice(0).join(", "));
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}
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function attempt(label: string, run: () => unknown): void {
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try {
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show(label, run());
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} catch (error) {
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console.log(label, error instanceof TypeError, (error as Error).message, log.splice(0).join(", "));
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}
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}
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const counter: any = new Counter();
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show("valueOf()", counter.valueOf());
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show("valueOf() again", counter.valueOf());
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show("toString()", counter.toString());
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show("total", (counter as Counter).total);
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const radix: any = new Radix(255);
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show("toString()", radix.toString());
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show("toString(16)", radix.toString(16));
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show("toString(2)", radix.toString(2));
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const plain: any = new Plain();
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show("plain valueOf", plain.valueOf() === plain);
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show("plain toString", plain.toString());
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const values: [string, any][] = [
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["number", 5],
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["string", "text"],
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["boolean", true],
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["bigint", 10n],
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["literal", { valueOf: () => 7 }],
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];
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for (const [label, value] of values) show(`${label} valueOf`, value.valueOf());
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const array: any = [1, 2];
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show("array valueOf", array.valueOf() === array);
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const object: any = { a: 1 };
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show("object valueOf", object.valueOf() === object);
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const dictionary: any = Object.create(null);
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attempt("dictionary valueOf", () => dictionary.valueOf());
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const missing: any = JSON.parse("null");
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attempt("null valueOf", () => missing.valueOf());
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const temperature: any = new Temperature(21);
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show("+", temperature + 1);
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show("==", temperature == 21);
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show("*", temperature * 2);
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show("<", temperature < 30);
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show("template", `${temperature}`);
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show("String", String(temperature));
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show("Number", Number(temperature));
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show("unary +", +temperature);
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const keyed: any = {};
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keyed[temperature] = "warm";
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show("key", Object.keys(keyed).join(","));
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const celsius: any = new Celsius(5);
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show("inherited +", celsius + 1);
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show("inherited template", `${celsius}`);
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show("own valueOf()", celsius.valueOf());
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const broken: any = new Broken();
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attempt("broken +", () => broken + 1);
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attempt("broken template", () => `${broken}`);
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