mirror of
https://github.com/vercel-labs/scriptc.git
synced 2026-10-22 05:59:31 +08:00
Chris Tate
94fd361b54
Represent ordinary JavaScript arrays with hole, value, and explicit-undefined states; add sparse side storage and carry missing values through the frontend, native backends, runtime, and Node-facing consumers.
69 lines
2.3 KiB
TypeScript
69 lines
2.3 KiB
TypeScript
// Ordinary dense-array reads keep JavaScript's undefined result at the
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// frontend boundary, including when TypeScript does not enable
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// noUncheckedIndexedAccess.
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const numbers: number[] = [10];
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const words: string[] = [];
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const refs: { name: string }[] = [{ name: "kept" }];
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console.log(`${numbers[1]}`, `${words[0]}`);
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console.log("string arithmetic", words[0] + 1, 1 + words[0], words[0] + words[0]);
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const storedStringArithmetic = words[3] + 2;
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function returnedStringArithmetic(values: string[]): number | string {
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return values[3] + 2;
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}
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const returnedStringArithmeticValue = returnedStringArithmetic(words);
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console.log("stored string arithmetic", typeof storedStringArithmetic, storedStringArithmetic, typeof returnedStringArithmeticValue, returnedStringArithmeticValue);
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console.log(numbers[1] ?? 42, words[0] || "missing", refs[1] === undefined);
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console.log(numbers[0], words[0], refs[0] === refs[0]);
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const numberMissing = numbers[1];
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const wordMissing = words[0];
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console.log(numberMissing === undefined, wordMissing === undefined);
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if (numberMissing === undefined) console.log("number narrowed");
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if (!wordMissing) console.log("word narrowed");
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const [head, tail] = numbers;
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const [firstWord, secondWord] = words;
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console.log(head, tail, firstWord, secondWord);
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const mutable: string[] = ["first"];
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const alias = mutable;
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const beforeMutation = mutable[0];
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alias.pop();
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console.log(beforeMutation ?? "missing", mutable[0] ?? "missing");
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console.log(["a", "b"].pop(), [].pop());
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console.log(["a", "b"].shift(), [].shift());
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const popped: number[] = [];
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console.log(popped.pop() ?? "empty", popped.shift() ?? "empty");
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let reads = 0;
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function take(empty: boolean): number[] {
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reads++;
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return empty ? [] : [4];
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}
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console.log(take(true)[0] === undefined, reads);
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console.log(take(false)[0] + 1, reads);
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console.log(take(false)[0] === take(false)[0], reads);
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function inspectNumber(value: number): void {
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console.log(typeof value, value, value + 1);
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}
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function firstNumber(values: number[]): number {
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return values[0];
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}
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const inspectAlias = inspectNumber;
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const firstAlias = firstNumber;
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inspectAlias(firstAlias([]));
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function firstOrMissing(xs: number[]): number | undefined {
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return xs[0];
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}
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function show(value: number | undefined): void {
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console.log(value === undefined ? "parameter missing" : value);
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}
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show(firstOrMissing([]));
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show(firstOrMissing([7]));
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