tmu
800c11139d
Drop the strict/widened aliases from src/index.ts so the factories are exported under their own names, and align the type tests, the autocomplete probe (which now imports the public surface from ./index.ts) and library.md with them. Also correct the widened-overload comment: the excess-property check does not apply to a generic P, so MatcherWidening's keyof guard — not the closed constraint — is what rejects keys outside T/_, as library.md already documented.
64 lines
2.6 KiB
TypeScript
64 lines
2.6 KiB
TypeScript
import type { ValueOf } from "type-fest";
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type UnaryFn<T, R> = (shape: T) => R;
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// `Extract` drops optional handlers (`undefined`) so `PatternReturns` also works
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// when `P`'s constraint has optional keys.
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type PatternReturns<P> = ReturnType<
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Extract<ValueOf<P>, (...args: never[]) => unknown>
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>;
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type Handlers<R, T extends string | number> = { [K in T]: UnaryFn<K, R> };
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// Fallback form: `_` is a required key, the T-keys are optional.
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type Fallback<R, T extends string | number> = Partial<Handlers<R, T>> & {
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_: UnaryFn<T, R>;
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};
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// Completion form: T-keys required, `_` optional. Overload #1, because
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// TypeScript takes the *first* overload as the contextual type for the popup.
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type ExhaustiveLoose<R, T extends string | number> = Handlers<R, T> & {
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_?: UnaryFn<T, R>;
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};
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// oxlint-disable typescript/unified-signatures
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// Strict returns: one common `R`. Overload order is load-bearing:
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// #1 ExhaustiveLoose -> autocomplete `_?, a, b`
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// #2 Fallback -> accepts a partial pattern
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// #3 Handlers (last) -> "Property 'b' is missing" is the reported error
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interface MatcherStrict<T extends string | number> {
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<R>(pattern: ExhaustiveLoose<R, T>): UnaryFn<T, R>;
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<R>(pattern: Fallback<R, T>): UnaryFn<T, R>;
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<R>(pattern: Handlers<R, T>): UnaryFn<T, R>;
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}
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// oxlint-enable typescript/unified-signatures
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// Widened returns: the union of every handler's return type. `P` is inferred
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// from the whole parameter, whose closed constraint supplies the
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// contextual/autocomplete type; the `keyof P` guard appended to each overload
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// rejects keys outside `T`/`_`.
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interface MatcherWidening<T extends string | number> {
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<P extends ExhaustiveLoose<unknown, T>>(
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pattern: P & (keyof P extends T | "_" ? unknown : never),
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): UnaryFn<T, PatternReturns<P>>;
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<P extends Fallback<unknown, T>>(
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pattern: P & (keyof P extends T | "_" ? unknown : never),
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): UnaryFn<T, PatternReturns<P>>;
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<P extends Handlers<unknown, T>>(
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pattern: P & (keyof P extends T | "_" ? unknown : never),
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): UnaryFn<T, PatternReturns<P>>;
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}
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type HandlerMap = Record<string | number, UnaryFn<never, unknown> | undefined>;
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const dispatch =
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(pattern: HandlerMap) =>
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(shape: string | number): unknown =>
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// oxlint-disable-next-line typescript/no-non-null-assertion typescript/no-unsafe-type-assertion
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(pattern[shape] ?? pattern["_"]!)(shape as never);
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export const getMatcher = <T extends string | number>(): MatcherStrict<T> =>
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dispatch;
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export const getMatcherW = <T extends string | number>(): MatcherWidening<T> =>
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dispatch;
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