mirror of
https://github.com/vercel-labs/scriptc.git
synced 2026-11-02 07:43:42 +08:00
Chris Tate
7943812231
A partial record assertion's literal now keeps the asserted type's optional fields it omits, in their absent state, as an ordinary record of that type does: a read yields undefined, in answers false and a write adds the property, with no guard. Only an omitted required field is missing from the view, and only its writes are guarded, so a write to an absent optional field of an ordinary record of the same type no longer throws. The receiver of a guarded write is saved whenever its value is, so a right side that reassigns the receiver's variable no longer redirects the check and the store.
66 lines
3.1 KiB
TypeScript
66 lines
3.1 KiB
TypeScript
// A partial `as` assertion keeps the literal's own layout and answers the
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// asserted type through a record view: fields the literal never wrote are
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// absent, and reflection sees exactly what Node sees.
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interface TruncationResult { content: string; truncated: boolean; truncatedBy: "lines" | "bytes" | null; totalLines: number; firstLineExceedsLimit: boolean }
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class Panel {
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private truncation?: TruncationResult;
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setComplete(truncation?: TruncationResult): void { this.truncation = truncation; }
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summary(): string { return `${this.truncation?.truncated ?? false}`; }
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dump(): string { return JSON.stringify(this.truncation ?? null); }
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keys(): string { return this.truncation ? Object.keys(this.truncation).join(",") : "-"; }
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hasContent(): boolean { return this.truncation !== undefined && "content" in this.truncation; }
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}
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function render(truncated: boolean, output: string): string {
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const a = new Panel();
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a.setComplete(truncated ? ({ truncated: true } as TruncationResult) : undefined);
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const b = new Panel();
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b.setComplete(truncated ? ({ truncated: true, content: output } as TruncationResult) : undefined);
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return [a.summary(), a.dump(), a.keys(), a.hasContent(), b.summary(), b.dump(), b.keys(), b.hasContent()].join(" ");
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}
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console.log(render(true, "out"));
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console.log(render(false, "out"));
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const full: TruncationResult = { content: "c", truncated: false, truncatedBy: null, totalLines: 3, firstLineExceedsLimit: false };
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const p = new Panel(); p.setComplete(full);
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console.log(p.summary(), p.dump(), p.keys(), p.hasContent(), full.totalLines + 1);
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// An optional field the literal omits reads as undefined, and `in` answers
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// false for it.
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interface Note { content: string; truncated: boolean; note?: string; count?: number }
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function note(flag: boolean): Note {
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return flag ? ({ truncated: true } as Note) : { content: "c", truncated: false, note: "n" };
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}
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const omitted = note(true);
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console.log(omitted.note, omitted.note ?? "none", omitted.count === undefined, typeof omitted.note);
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console.log("note" in omitted, "truncated" in omitted, "content" in omitted);
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const written = note(false);
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console.log(written.note, "note" in written, "count" in written);
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// A write of a field the literal omits evaluates its right side first.
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const order: string[] = [];
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function rhs(): string {
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order.push("rhs");
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return "v";
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}
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const target = note(true);
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try {
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target.content = rhs();
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} catch {
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order.push("caught");
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}
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console.log(order[0]);
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// An ordinary record of the asserted type keeps a slot for its absent
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// optional field, so a write adds the property.
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const plainNote: Note = { content: "c", truncated: false };
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plainNote.note = "added";
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console.log(plainNote.note, "note" in plainNote, JSON.stringify(plainNote));
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// A right side that reassigns the receiver's variable: the original
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// receiver takes the write.
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let reassigned: Note = { content: "first", truncated: false, note: "n" };
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const firstNote = reassigned;
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const otherNote: Note = { content: "other", truncated: true, note: "o" };
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reassigned.content = ((reassigned = otherNote), "changed");
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console.log(firstNote.content, otherNote.content, reassigned === otherNote);
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export {};
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