feature request: readonly only outside and writable inside

[LongTengDao]

Search Terms

Suggestion

Sometime we need a value readonly from outside, but writable of cause inside. Usually we do it by double properties, but that's superfluous and waste of performance.

Use Cases

export default class Foo {

    private _value1;
    protected get value1 () { return this._value1; }

    private _value2;
    public get value2 () { return this._value2; }

    protected _value3;
    public get value3 () { return this._value3; }

};

We do all things above to make sure the value could only write from inside, otherwise, there will be a TS warn. If we want to save performance (ignore the superfluous problem being worse):

declare class _Foo {
    protected readonly value1;
    readonly value2;
    readonly value3;
}
const Foo = class {
    value1;
    value2;
    value3;
} as typeof _Foo;
type Foo = _Foo;
export { Foo as default };

Examples

One solution (everyone can suggest a better one of cause, I mainly point out the need):

export default class Foo {
    protected private value1;
    public private value2;
    public protected value3;
};

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.

[MartinJohns]

Duplicate of #37487.