Item 57: Prefer Tail-Recursive Generic Types

要点

Aim to make your recursive generic types tail recursive. They're more efficient and have greater depth limits.
Recursive type aliases can often be made tail recursive by rewriting them to use an accumulator.
旨在使递归泛型类型尾递归。尾递归更加高效，且具有更大的深度限制。
通过重写递归类型别名，使其使用累加器，可以将其转换为尾递归形式。

正文

function sum(nums: readonly number[]): number {
  if (nums.length === 0) {
    return 0
  }
  return nums[0] + sum(nums.slice(1))
}

console.log(sum([0, 1, 2, 3, 4]))

💻 playground

const arr = Array(7875).fill(1)
console.log(sum(arr))

💻 playground

function sum(nums: readonly number[], acc = 0): number {
  if (nums.length === 0) {
    return acc
  }
  return sum(nums.slice(1), nums[0] + acc)
}

💻 playground

type GetChars<S extends string> =
  S extends `${infer FirstChar}${infer RestOfString}`
    ? FirstChar | GetChars<RestOfString>
    : never

type ABC = GetChars<'abc'>
//   ^? type ABC = "a" | "b" | "c"

💻 playground

type Long = GetChars<'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWX'>
//          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
//          Type instantiation is excessively deep and possibly infinite.

💻 playground

type ToSnake<T extends string> = string extends T
  ? string // We want ToSnake<string> = string
  : T extends `${infer First}${infer Rest}`
  ? First extends Uppercase<First> // Is First a capital letter?
    ? `_${Lowercase<First>}${ToSnake<Rest>}` // e.g. "B" -> "_b"
    : `${First}${ToSnake<Rest>}`
  : T

type S = ToSnake<'fooBarBaz'>
//   ^? type S = "foo_bar_baz"

type Two = ToSnake<'className' | 'tagName'>
//   ^? type Two = "class_name" | "tag_name"

💻 playground

type Long = ToSnake<'reallyDescriptiveNamePropThatsALittleTooLoquacious'>
//          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
//          Type instantiation is excessively deep and possibly infinite.

💻 playground

type ToSnake<T extends string, Acc extends string = ''> = string extends T
  ? string // We want ToSnake<string> = string
  : T extends `${infer First}${infer Rest}`
  ? ToSnake<
      Rest,
      First extends Uppercase<First>
        ? `${Acc}_${Lowercase<First>}`
        : `${Acc}${First}`
    >
  : Acc

type S = ToSnake<'fooBarBaz'>
//   ^? type S = "foo_bar_baz"

type Two = ToSnake<'className' | 'tagName'>
//   ^? type Two = "class_name" | "tag_name"

type Long = ToSnake<'reallyDescriptiveNamePropThatsALittleTooLoquacious'>
//   ^? type Long = "really_descriptive_name_prop_thats_a_little_too_loquacious"

💻 playground

Item 57: Prefer Tail-Recursive Generic Types ​

要点 ​

正文 ​

Item 57: Prefer Tail-Recursive Generic Types

要点

正文