题目描述
实现Capitalize<T>它将字符串的第一个字母转换为大写，其余字母保持原样。
例如
type capitalized = Capitalize<'hello world'> // expected to be 'Hello world'
题解
// ============= Test Cases =============
import type { Equal, Expect } from './test-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'>>,
]
// ============= Your Code Here =============
type MyCapitalize<T extends string> =
T extends `${infer Head}${infer Tail}`
? `${Uppercase<Head>}${Tail}`
: T
类型约束
使用T extends string对类型T进行约束，确保T是一个字符串类型
条件类型
T extends `${infer Head}${infer Tail}`
? `${Uppercase<Head>}${Tail}`
: T
- T extends
${infer Head}${infer Tail}是一个条件类型，检查T是否是非空字符串infer Head用于推断出T的第一个字符infer Tail用于推断出T的剩余字符
${Uppercase<Head>}${Tail}将第一个字符Head转换为大写，然后与剩余字符Tail拼接成新的字符串- 如果
T为空字符串，则返回T本身
