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Provide a modifier to allow classes to protect property state while allowing mutations/changes within the class #39461

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@Jonathan002

Description

@Jonathan002

Search Terms

"modify readonly for internal classes" - leads to "as any" hack (Goal is to create convinience)
"protected" search - can only be read by derived classes

Suggestion

I find myself looking to complex solutions or longer code to protect state. I'm hoping typescript can be used to reduce code and protect state away from runtime through a public readonly modifier that has write access for internal methods of a class.

Use Cases

I'm hoping to save runtime through typing state protection and avoid extra code such as getters and frameworks that use runtime to manage state.

Examples

class Dog {
    readonlyPublic asleep = true
   wake() {
       // console.trace();
       this.asleep = false; // will not throw an error as expected with "readonly"
   }
}

const dogA = new Dog();
dogA.asleep = false // Error this is readonlyPublic (forcing us to use the dogA.wake() method to update state)
const isDogAsleep = dogA.asleep // but we can read it publicly without an error..
console.log(isDogAsleep) // => true

-------- update state
dogA.wake();
console.log(dogA.asleep) // => false;

Checklist

My suggestion meets these guidelines:

  • 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, etc.)
  • This feature would agree with the rest of TypeScript's Design Goals.

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    DeclinedThe issue was declined as something which matches the TypeScript visionSuggestionAn idea for TypeScript

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