private fields in nested classes should have separate types?

🔍 Search Terms

typescript private field nested class

✅ Viability Checklist

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

⭐ Suggestion

Private fields of a wrapper class are similar to symbols: perhaps the nested classes could have their own types for the fields based on the value they initialize in their constructor:

📃 Motivating Example

https://www.typescriptlang.org/play/?noImplicitAny=false#code/MYGwhgzhAEBiBOBLApgOwCYwN4CgCQAxAG5ggCuyO+sA9jdALzSiQy33IAeALmpnEj7Z8eYDVQRu8MsG414ACgCU0XHnUQyAB2SKlIvNwAWiCADpipCo2gAWAKwA2aAHoX0ADwBaH779foVDIAWwAjXREAXyp1ADM6AFlkYxp0ZVUDMQkaEGQzEBoAcwVjUwsScmR9dWi8aPwAITB4GxYoaCaWrl4MGFLzdgz1LMlpWXl0tQ1tXWUDfvKrZBsAIgB2AA4AThXXd29-Q59oUcRUQqiYvFDmpJS0lSnRcQgcvILihctK6rr8aPqI24qnYABoOs1IjZUMgAO4CFC9OY4IHQWLQuFwOhzVGhDHwzrI2JmeI0O5GVLpNzQD4wFYORwrHChMw3eDkykqam06DrbYrIA

Plain JS:

class Friends {
	#priv

	Foo = class Foo extends Friends {
		constructor() {
			super()
			this.#priv = 456 // <----------- number
		}

		fooMethod() {
			console.log(this.#priv)
		}
	}

	Bar = class Bar extends this.Foo {
		constructor() {
			super()
			this.#priv = "789" // <-------------- string
		}

		barMethod() {
			console.log(this.#priv)
		}
	}
}

const {Foo, Bar} = new Friends()

const f = new Foo()
const b = new Bar()

f.fooMethod() // logs "456"
b.barMethod() // logs "789"

💻 Use Cases

Allows having a "private" key to use on multiple classes, but each class could have a different type of value.

Inizia con l’esempio collegato di TypeScript Playground e verifica come vengono attualmente controllati i private fields nelle classi annidate e nelle relative classi ereditate. L’issue non indica file sorgente né test; per completarla sarebbero necessari un design concordato del type-system, oltre all’implementazione e ai test per i tipi di campo separati proposti.