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Malte UblandClaude Opus 5.5
815ce664e5
`let f: T; f = (n) => ... f(n - 1)` at module scope threw "Cannot access 'f' before initialization": a function-typed (pointer-guarded) binding kept the null-pointer TDZ test on its writes, but the declaration already initialized it (to undefined) when it ran. Such bindings now carry the existing initialization flag: the declaration sets it, writes that can run earlier check it, and writes no longer test the empty pointer. A write that really precedes the declaration still throws. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
47 lines
1.3 KiB
TypeScript
47 lines
1.3 KiB
TypeScript
// A module-scope `let` declared without an initializer is initialized (to
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// undefined) where the declaration runs, so a later assignment of a closure
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// that calls the binding itself is an ordinary write.
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type Step = (n: number) => number;
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// A write that runs before the declaration is still in the dead zone.
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function early(): void {
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late = () => 1;
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}
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try {
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early();
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} catch (e) {
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console.log((e as Error).name, (e as Error).message);
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}
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let late: () => number;
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late = () => 2;
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early();
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console.log(late());
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let countdown: Step;
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countdown = (n) => (n <= 0 ? 0 : 1 + countdown(n - 1));
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console.log(countdown(5));
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let log: (s: string) => void;
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log = (s) => {
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if (s.length < 3) log(s + "!");
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else console.log(s);
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};
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log("a");
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// Reassignment and assignment from a function body after the declaration.
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let pick: (xs: number[]) => number;
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function install(largest: boolean): void {
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pick = largest ? (xs) => Math.max(...xs) : (xs) => Math.min(...xs);
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}
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install(true);
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console.log(pick!([3, 9, 4]));
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install(false);
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console.log(pick!([3, 9, 4]));
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// Mutual recursion through two such bindings.
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let isEven: (n: number) => boolean;
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let isOdd: (n: number) => boolean;
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isEven = (n) => (n === 0 ? true : isOdd(n - 1));
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isOdd = (n) => (n === 0 ? false : isEven(n - 1));
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console.log(isEven(10), isOdd(7), isEven(3));
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