Item 40: Prefer Imprecise Types to Inaccurate Types

要点

Avoid the uncanny valley of type safety: complex but inaccurate types are often worse than simpler, less precise types. If you cannot model a type accurately, do not model it inaccurately! Acknowledge the gaps using any or unknown.
Pay attention to error messages and autocomplete as you make typings increasingly precise. It's not just about correctness: developer experience matters, too.
As your types grow more complex, your test suite for them should expand.
避免类型安全的“怪异谷”：复杂但不准确的类型通常比简单、不精确的类型更糟。如果无法准确建模类型，就不要不准确地建模！可以使用 any 或 unknown 来承认类型模型中的空白。
在使类型越来越精确时，关注错误信息和自动补全功能。这不仅仅关乎正确性：开发者体验同样重要。
随着类型变得更加复杂，针对这些类型的测试用例也应当增加。

正文

interface Point {
  type: 'Point'
  coordinates: number[]
}
interface LineString {
  type: 'LineString'
  coordinates: number[][]
}
interface Polygon {
  type: 'Polygon'
  coordinates: number[][][]
}
type Geometry = Point | LineString | Polygon // Also several others

💻 playground

type GeoPosition = [number, number]
interface Point {
  type: 'Point'
  coordinates: GeoPosition
}
// Etc.

💻 playground

type Expression1 = any
type Expression2 = number | string | any[]

💻 playground

const okExpressions: Expression2[] = [
  10,
  'red',
  ['+', 10, 5],
  ['rgb', 255, 128, 64],
  ['case', ['>', 20, 10], 'red', 'blue'],
]
const invalidExpressions: Expression2[] = [
  true,
  // ~~~ Type 'boolean' is not assignable to type 'Expression2'
  ['**', 2, 31], // Should be an error: no "**" function
  ['rgb', 255, 0, 127, 0], // Should be an error: too many values
  ['case', ['>', 20, 10], 'red', 'blue', 'green'], // (Too many values)
]

💻 playground

type FnName = '+' | '-' | '*' | '/' | '>' | '<' | 'case' | 'rgb'
type CallExpression = [FnName, ...any[]]
type Expression3 = number | string | CallExpression

const okExpressions: Expression3[] = [
  10,
  'red',
  ['+', 10, 5],
  ['rgb', 255, 128, 64],
  ['case', ['>', 20, 10], 'red', 'blue'],
]
const invalidExpressions: Expression3[] = [
  true,
  // Error: Type 'boolean' is not assignable to type 'Expression3'
  ['**', 2, 31],
  // ~~ Type '"**"' is not assignable to type 'FnName'
  ['rgb', 255, 0, 127, 0], // Should be an error: too many values
  ['case', ['>', 20, 10], 'red', 'blue', 'green'], // (Too many values)
]

💻 playground

type Expression4 = number | string | CallExpression

type CallExpression = MathCall | CaseCall | RGBCall

type MathCall = ['+' | '-' | '/' | '*' | '>' | '<', Expression4, Expression4]

interface CaseCall {
  0: 'case'
  [n: number]: Expression4
  length: 4 | 6 | 8 | 10 | 12 | 14 | 16 // etc.
}

type RGBCall = ['rgb', Expression4, Expression4, Expression4]

💻 playground

const okExpressions: Expression4[] = [
  10,
  'red',
  ['+', 10, 5],
  ['rgb', 255, 128, 64],
  ['case', ['>', 20, 10], 'red', 'blue'],
]
const invalidExpressions: Expression4[] = [
  true,
  // ~~~ Type 'boolean' is not assignable to type 'Expression4'
  ['**', 2, 31],
  // ~~~~ Type '"**"' is not assignable to type '"+" | "-" | "/" | ...
  ['rgb', 255, 0, 127, 0],
  //                   ~ Type 'number' is not assignable to type 'undefined'.
  ['case', ['>', 20, 10], 'red', 'blue', 'green'],
  // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  // Types of property 'length' are incompatible.
  //    Type '5' is not assignable to type '4 | 6 | 8 | 10 | 12 | 14 | 16'.
]

💻 playground

const moreOkExpressions: Expression4[] = [
  ['-', 12],
  // ~~~~~~ Type '["-", number]' is not assignable to type 'MathCall'.
  //          Source has 2 element(s) but target requires 3.
  ['+', 1, 2, 3],
  //          ~ Type 'number' is not assignable to type 'undefined'.
  ['*', 2, 3, 4],
  //          ~ Type 'number' is not assignable to type 'undefined'.
]

💻 playground

Item 40: Prefer Imprecise Types to Inaccurate Types ​

要点 ​

正文 ​

Item 40: Prefer Imprecise Types to Inaccurate Types

要点

正文