26. Capitalize

[astak16]

题目

题目链接：Capitalize

实现 MyCapitalize，满足下面要求

import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<MyCapitalize<'foobar'>, 'Foobar'>>,
  Expect<Equal<MyCapitalize<'FOOBAR'>, 'FOOBAR'>>,
  Expect<Equal<MyCapitalize<'foo bar'>, 'Foo bar'>>,
  Expect<Equal<MyCapitalize<''>, ''>>,
  Expect<Equal<MyCapitalize<'a'>, 'A'>>,
  Expect<Equal<MyCapitalize<'b'>, 'B'>>,
  Expect<Equal<MyCapitalize<'c'>, 'C'>>,
  Expect<Equal<MyCapitalize<'d'>, 'D'>>,
  Expect<Equal<MyCapitalize<'e'>, 'E'>>,
  Expect<Equal<MyCapitalize<'f'>, 'F'>>,
  Expect<Equal<MyCapitalize<'g'>, 'G'>>,
  Expect<Equal<MyCapitalize<'h'>, 'H'>>,
  Expect<Equal<MyCapitalize<'i'>, 'I'>>,
  Expect<Equal<MyCapitalize<'j'>, 'J'>>,
  Expect<Equal<MyCapitalize<'k'>, 'K'>>,
  Expect<Equal<MyCapitalize<'l'>, 'L'>>,
  Expect<Equal<MyCapitalize<'m'>, 'M'>>,
  Expect<Equal<MyCapitalize<'n'>, 'N'>>,
  Expect<Equal<MyCapitalize<'o'>, 'O'>>,
  Expect<Equal<MyCapitalize<'p'>, 'P'>>,
  Expect<Equal<MyCapitalize<'q'>, 'Q'>>,
  Expect<Equal<MyCapitalize<'r'>, 'R'>>,
  Expect<Equal<MyCapitalize<'s'>, 'S'>>,
  Expect<Equal<MyCapitalize<'t'>, 'T'>>,
  Expect<Equal<MyCapitalize<'u'>, 'U'>>,
  Expect<Equal<MyCapitalize<'v'>, 'V'>>,
  Expect<Equal<MyCapitalize<'w'>, 'W'>>,
  Expect<Equal<MyCapitalize<'x'>, 'X'>>,
  Expect<Equal<MyCapitalize<'y'>, 'Y'>>,
  Expect<Equal<MyCapitalize<'z'>, 'Z'>>,
]

答案

方法一

type MyCapitalize<T extends string> = T extends `${infer F}${infer Rest}`
  ? `${Uppercase<F>}${Rest}`
  : T;

方法二

type AlphaMap = {
  a: "A";
  b: "B";
  c: "C";
  d: "D";
  e: "E";
  f: "F";
  g: "G";
  h: "H";
  i: "I";
  j: "J";
  k: "K";
  l: "L";
  n: "N";
  m: "M";
  o: "O";
  p: "P";
  q: "Q";
  r: "R";
  s: "S";
  t: "T";
  u: "U";
  v: "V";
  w: "W";
  x: "X";
  y: "Y";
  z: "Z";
}

type MyUppercase<T extends string> = T extends `${infer F}${infer Rest}`
  ? F extends keyof AlphaMap
    ? `${AlphaMap[F]}${Rest}`
    : T
  : T;

知识点

自己实现 Uppercase

有一点需要注意：F extends keyof AlphaMap 保证 F 是小写字母