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https://github.com/vercel-labs/scriptc.git
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Chris Tate
8b6d3329f4
When the index assigns the receiver's binding (`a[(a = b, 0)] = c[0]!`), holding the index alone left the receiver read at the store, after the index ran, so the value landed in the replacement array. The receiver is now held whenever the index or the value could change what it reads.
46 lines
1.3 KiB
TypeScript
46 lines
1.3 KiB
TypeScript
// An element assignment evaluates its receiver and index before its value,
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// also when the value is an optional element read or a call that assigns
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// the bindings the receiver and index read.
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const a = [10, 20, 30, 40];
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const b = [1, 2, 3, 4];
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let n = 0;
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a[n++] = b[n]!;
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console.log(a.join(), n);
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a[n] = b[n++];
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console.log(a.join(), n);
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const optional: (number | undefined)[] = [undefined, 5, undefined];
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let k = 0;
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optional[k++] = optional[k];
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console.log(optional, k);
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// A call in the value assigns the receiver and the index through closures.
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let target: (number | undefined)[] = [0, 0, 0];
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const first = target;
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let at = 0;
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function swap(): number | undefined {
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target = [9, 9, 9];
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at = 2;
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return b[3];
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}
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target[at] = swap();
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console.log(first, target, at);
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// The index and receiver are not evaluated twice.
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let reads = 0;
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function index(): number {
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reads++;
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return 1;
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}
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const c: (number | undefined)[] = [0, 0];
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c[index()] = optional[1];
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console.log(c, reads);
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// The index assigns the receiver's binding: the store uses the receiver
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// evaluated before it.
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let receiver: (number | undefined)[] = [0, 0];
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const original = receiver;
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const replacement: (number | undefined)[] = [7, 7];
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receiver[((receiver = replacement), 1)] = optional[1];
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console.log(original, replacement, receiver === replacement);
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