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https://github.com/vercel-labs/scriptc.git
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Chris Tate
8d2b3bb2e0
- lowerUnitComparison folds ===/!== against a union lacking the unit arm to the constant answer, both operand orders - a non-droppable operand still evaluates exactly once, riding a throwaway tag test - union-switch case null / case undefined take the unit-comparison lowering, so a lacking arm never matches - the unionEq fallback had coerced the literal through the stranded-arm trap, throwing where Node answers false - corpus 2490-2494: the find-miss repro, every strict and loose spelling, switch unit cases, effect preservation
27 lines
859 B
TypeScript
27 lines
859 B
TypeScript
// The no-arm unit comparison still EVALUATES its operand: `xs.find(probe) === null` runs the probe callbacks (JS evaluates both sides of ===), the answer is the constant, and `??` on `T | undefined` / `T | null` takes the default on exactly its own unit arms.
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let calls = 0;
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const xs = [1, 2, 3];
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const probe = (x: number): boolean => {
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calls++;
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return x > 10;
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};
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console.log(xs.find(probe) === null);
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console.log(calls);
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console.log(xs.find(probe) !== null);
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console.log(calls);
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console.log(null === xs.find(probe));
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console.log(calls);
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function pick(): number | undefined {
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calls += 100;
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return undefined;
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}
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console.log(pick() === null, calls);
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console.log(pick() ?? -1);
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function pickNull(): string | null {
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calls += 1000;
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return null;
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}
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console.log(pickNull() === undefined, calls);
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console.log(pickNull() ?? "fallback");
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console.log(calls);
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