Replace First

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题目

Implement the type ReplaceFirst<T, S, R> which will replace the first occurrence of S in a tuple T with R. If no such S exists in T, the result should be T.

/* _____________ 测试用例 _____________ */
import type { Equal, Expect } from "@type-challenges/utils";

type cases = [
  Expect<Equal<ReplaceFirst<[1, 2, 3], 3, 4>, [1, 2, 4]>>,
  Expect<Equal<ReplaceFirst<["A", "B", "C"], "C", "D">, ["A", "B", "D"]>>,
  Expect<
    Equal<ReplaceFirst<[true, true, true], true, false>, [false, true, true]>
  >,
  Expect<
    Equal<
      ReplaceFirst<[string, boolean, number], boolean, string>,
      [string, string, number]
    >
  >,
  Expect<Equal<ReplaceFirst<[1, "two", 3], string, 2>, [1, 2, 3]>>,
  Expect<
    Equal<
      ReplaceFirst<["six", "eight", "ten"], "eleven", "twelve">,
      ["six", "eight", "ten"]
    >
  >
];

解答

type ReplaceFirst<T extends readonly unknown[], S, R> = T extends readonly [
  infer F,
  ...infer Rest
]
  ? F extends S
    ? [R, ...Rest]
    : [F, ...ReplaceFirst<Rest, S, R>]
  : [];