mirror of
https://github.com/vercel-labs/scriptc.git
synced 2026-10-28 06:53:42 +08:00
Malte Ubl
b4134160f4
`a.splice(i, n, v)` where v may hold undefined at run time (a for-of binding or unchecked read, as in reorderCandidates) always built a present-undefined item array. It now evaluates receiver, start, count, and v once, in order, and branches: a present v is spliced as a plain element literal, a missing one keeps the item array. In statement position the emitter now also looks through such sequences and conditionals, so the present arm drops its removed elements with scr_arr_splice_drop and allocates nothing.
88 lines
2.8 KiB
TypeScript
88 lines
2.8 KiB
TypeScript
// splice() inserting one value that may be a hole or missing read: present
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// values insert as themselves, missing ones as present undefined, in
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// statement position and when the removed elements are used. Evaluation
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// order and reference lifetimes must match Node.
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class Sig {
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name: string;
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constructor(name: string) {
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this.name = name;
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}
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}
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function show(list: readonly Sig[]): string {
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const parts: string[] = [];
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for (let i = 0; i < list.length; i++) {
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parts.push(i in list ? (list[i] === undefined ? "undef" : list[i]!.name) : "hole");
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}
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return `${list.length}:[${parts.join(",")}]`;
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}
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// The reorderCandidates shape: insert each candidate at a computed index.
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const candidates: Sig[] = [new Sig("a"), new Sig("b")];
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candidates[3] = new Sig("d");
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candidates.push(new Sig("e"));
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const ordered: Sig[] = [];
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let index = 0;
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for (const sig of candidates) {
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ordered.splice(index % 2 === 0 ? 0 : ordered.length, 0, sig);
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index++;
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}
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console.log("ordered", show(ordered));
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// Unchecked reads as items, replacing and removing.
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const source: Sig[] = [new Sig("s0")];
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source[2] = new Sig("s2");
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const target: Sig[] = [new Sig("t0"), new Sig("t1"), new Sig("t2")];
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target.splice(1, 1, source[0]);
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target.splice(-1, 1, source[1]);
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target.splice(99, 0, source[2]);
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target.splice(0, 0, source[7]);
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console.log("reads", show(target));
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// The removed elements are observed.
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const removed = target.splice(1, 2, source[1]);
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const removed2 = target.splice(0, 1, source[0]);
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console.log("removed", show(removed), show(removed2), show(target));
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// Evaluation order: receiver, start, count, item.
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const log: string[] = [];
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const at = (label: string, value: number): number => {
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log.push(label);
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return value;
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};
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const read = (label: string, i: number): Sig => {
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log.push(label);
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return source[i]!;
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};
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target.splice(at("start", 1), at("count", 1), read("item", 2));
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console.log("order", log.join(","), show(target));
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// The item expression reassigns the receiver variable.
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let list: Sig[] = [new Sig("l0"), new Sig("l1")];
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const original = list;
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const other: Sig[] = [];
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list.splice(1, 0, ((list = other), source[0]));
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console.log("reassigned", show(original), show(other), list === other);
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// Numbers and strings from hole-observing loops.
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const nums: number[] = [1];
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nums[2] = 3;
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const numsOut: number[] = [9];
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for (const n of nums) numsOut.splice(1, 0, n);
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const words: string[] = ["w"];
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words[2] = "y";
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const wordsOut: string[] = [];
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for (const w of words) wordsOut.splice(0, 0, w);
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console.log("scalars", JSON.stringify(numsOut), JSON.stringify(wordsOut), 1 in numsOut);
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// A dropped source keeps inserted elements alive.
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function collect(): Sig[] {
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const temp: Sig[] = [new Sig("x"), new Sig("y")];
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const out: Sig[] = [];
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for (const sig of temp) out.splice(0, 0, sig);
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temp.length = 0;
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return out;
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}
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console.log("collected", show(collect()));
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