Generic type on class prevents access of protected entries with explicitly typed 'this' function argument

[adekau]

TypeScript Version: Tested on 3.2.4, 3.6.3, 3.8.0-dev.20191112

Search Terms: Property, protected, accessible, through, instance, generics, decorator

Code

class Accessor<T> {
    private _properties: { [key: string]: any } = {};

    constructor() { }

    protected _get(key: string): any {
        return this._properties[key];
    }

    protected _set(key: string, value: any): void {
        this._properties[key] = value;
    }
}

function property() {
    return function (target: any, key: string): void {
        const getter = function (this: Accessor<any>) { return this._get('something')}
    };
}

Expected behavior: Should allow access to protected function _get since this is typed as an instance of the class Accessor.

Actual behavior:

index.ts:17:69 - error TS2446: Property '_get' is protected and only accessible through an instance of class 'Accessor<any>'.

17         const getter = function (this: Accessor<any>) { return this._get('something')}
                                                                       ~~~~

Note: this does not occur without the generic type on Accessor. If it is just class Accessor with function (this: Accessor) there is no error on calling this._get('something').

Playground Link: Playground Link

Related Issues: #10302, Potentially a duplicate of #29132. This was supposedly fixed in #24645 however it is problematic with generics as mentioned above.

[andrewbranch]

This is a better description of the problem, but it is indeed a duplicate of #29132.

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.