microsoft / microsoft/TypeScript

const/readonly assertion support for `Map` and `Set`

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#62,312 3 comentarios 1 reacción 0 asignados Ver en GitHub

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Go
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Merge medio
2 d 4 h
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Descripción

### 🔍 Search Terms

"as const", "as readonly", "const assertion", "keyed collections"

### ✅ Viability Checklist

- [x] This wouldn't be a breaking change in existing TypeScript/JavaScript code
- [x] This wouldn't change the runtime behavior of existing JavaScript code
- [x] This could be implemented without emitting different JS based on the types of the expressions
- [x] This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
- [x] This isn't a request to add a new utility type: https://github.com/microsoft/TypeScript/wiki/No-New-Utility-Types
- [x] This feature would agree with the rest of our Design Goals: https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals

### ⭐ Suggestion

Have a way to take an existing `Map` or `Set` and assert it to be its readonly variant without needing to repeat the generic types.

### 📃 Motivating Example

Today we can create maps (and sets) with explicit and inferred generic types but in order to make them readonly the generic types have to be explicitly written, sometimes repeated:

```ts
const exampleMap1: ReadonlyMap = new Map([["a", 1], ["b", 2]]);
const exampleMap2: ReadonlyMap = new Map().set('a', 1).set('b', 2);
```

With something like const assertion support for `Map` (and `Set`) we'd be able to get readonly maps and sets without repeating the generic types:

```ts
const exampleMap1 = new Map([["a", 1], ["b", 2]]) as const;
const exampleMap2 = new Map().set("a", 1).set("b", 2) as const;
```

### 💻 Use Cases

1. What do you want to use this for? I want to use this for creating keyed collections that will be used elsewhere and I want to avoid modifications. (Note: this won't prevent runtime modifications but the same is true for const assertions on arrays and objects today.)
2. What shortcomings exist with current approaches? Repetative generic types and verbose code to make a keyed collection readonly.
3. What workarounds are you using in the meantime? Repeating the generic types and explicitly defining things as readonly keyed collections.

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  1. Lee el issue completo y luego la guía de contribución del proyecto.
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  4. Abre un pull request que haga referencia al número del issue.

Línea de trabajo

Comienza revisando el comportamiento de las aserciones const de TypeScript para arrays y objetos, así como las reglas existentes de comprobación de tipos para Map y Set. Determina cómo deben representarse las colecciones con claves readonly sin repetir los tipos genéricos y, después, añade cobertura que demuestre que las aserciones propuestas infieren tipos Map y Set readonly, conservando al mismo tiempo la salida actual de JavaScript.

Escrito por el modelo de indexación a partir del texto del issue.

Evaluación

Stack tecnológico
typescript
Área
compilers
Tipo de issue
Nueva funcionalidad
Dificultad
5/5
Tiempo estimado
Más de una semana
Estado de actividad
Estancado
Claridad
Bastante claro
Aptitud para principiantes
25/100

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