mirror of
https://github.com/vercel-labs/scriptc.git
synced 2026-10-23 06:10:02 +08:00
Chris Tate
fc84780ebe
- a !-asserted (or SPI-off) field first assigned past the constructor's top level rides an undefined-armed union slot: allocation writes the interned undefined, writes wrap, reads extract the declared type - scalar reads take unit defaults where JS-undefined behavior survives (bool false, f64 NaN — conditions and arithmetic exact); string/ref reads keep the checked-extraction trap, JS's own first-member-use TypeError named earlier - union/map/dyn-typed ! fields keep the fence; deferral propagates down the base chain with the fields map - diagnostics fixtures re-pin the surviving fences; corpus 2429 pins the Output.initialize idiom on both backends; SEMANTICS.md 372-375
36 lines
971 B
TypeScript
36 lines
971 B
TypeScript
// A project tsconfig with strictPropertyInitialization OFF (strict: false;
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// strictNullChecks stays on — the floor): tsc no longer verifies that
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// initializer-less fields are assigned in the constructor. An
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// unconditionally ctor-assigned field compiles as ever (`Ok`); a field
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// assigned only in a method now DEFERS like a `!` assertion (the slot
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// rides `T | undefined`, reads extract — SEMANTICS.md 372), so `Bad`
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// compiles too. The fence survives exactly where the deferral cannot
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// carry the type: a MAP-typed field (map arms cannot join a union).
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class Ok {
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n: number;
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s: string;
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constructor(n: number) {
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this.n = n;
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this.s = "ok";
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}
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}
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class Bad {
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v: number; // compiles: deferred init (reads NaN until assigned)
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m(): void {
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this.v = 1;
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}
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}
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class Worse {
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m: Map<string, number>; // fenced: no deferral union for map fields
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fill(): void {
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this.m = new Map();
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}
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}
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console.log(new Ok(5).n);
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new Bad();
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new Worse();
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