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| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 | 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 6x 6x 6x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 2x 2x 2x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x | /**
* Pattern matching primitives. Each constructor returns a lightweight
* matcher object whose `matches` method returns a type guard.
*/
export interface Matcher<T> {
readonly matches: (value: unknown) => value is T;
}
const literalMatcher = <
const L extends string | number | boolean | null | undefined,
>(
value: L,
): Matcher<L> => ({
matches: (candidate): candidate is L => candidate === value,
});
const typeMatcher = <T>(
type:
| "string"
| "number"
| "boolean"
| "bigint"
| "symbol"
| "undefined"
| "object"
| "function",
): Matcher<T> => {
const matches = (value: unknown): value is T => {
if (type === "undefined") {
return value === undefined;
}
if (type === "object") {
return (
(typeof value === "object" && value !== null) ||
typeof value === "function"
);
}
return typeof value === type;
};
return { matches };
},
whenMatcher = <T>(
predicate: (value: unknown) => value is T,
): Matcher<T> => ({
matches: predicate,
}),
whenMatcherAny = <T>(
predicate: (value: unknown) => boolean,
): Matcher<T> => ({
matches: (value: unknown): value is T => predicate(value),
}),
isNestedMatcher = (expected: unknown): expected is Matcher<unknown> =>
typeof expected === "object" &&
expected !== null &&
"matches" in expected,
// oxlint-disable-next-line typescript/no-unnecessary-type-parameters
keysMatch = <S extends object>(shape: S, candidate: object): boolean => {
// oxlint-disable-next-line typescript/no-unsafe-type-assertion
for (const key of Object.keys(shape) as (keyof S)[]) {
if (!(key in candidate)) {
return false;
}
// oxlint-disable-next-line typescript/no-unsafe-type-assertion
const expected = shape[key],
// oxlint-disable-next-line typescript/no-unsafe-type-assertion
actual = candidate[key as keyof object];
if (isNestedMatcher(expected)) {
if (!expected.matches(actual)) {
return false;
}
} else if (actual !== expected) {
return false;
}
}
return true;
},
structuralMatcher = <S extends object, T extends S>(
shape: S,
refine?: (value: S) => value is T,
): Matcher<T> => ({
matches: (value: unknown): value is T => {
if (typeof value !== "object" || value === null) {
return false;
}
// oxlint-disable-next-line typescript/no-unsafe-type-assertion
const candidate = value as S;
if (!keysMatch(shape, candidate)) {
return false;
}
if (refine && !refine(candidate)) {
return false;
}
return true;
},
});
export const P = {
literal: literalMatcher,
type: typeMatcher,
when: whenMatcher,
any: whenMatcherAny,
shape: structuralMatcher,
} as const;
export type Pattern<T> = Matcher<T>;
|