I have a generic base service for performing CRUD operations where sub classes specify a specific entity (they also specify a respective end point url). The base class declares a protected api url that each sub class then initializes accordingly in the constructor.

Now I came across the need to actually change the signature of one of the operations for a specific entity, namely adding some parameters to get.

So I followed this to create a type without the get and than provide a new signature. This works, but now the protected api url property does not exist anymore, which I don't understand.

I created a boiled down example to demonstrate this here.

This is the code (errors in SubClass2):

interface Type1 {
    name: string;
}

interface Type2 {
    price: number;
}

class Service1 {}

class BaseClass<T> {
    protected prop1: string = 'BaseClass';

    constructor(protected dep1: Service1) {}

    foo(){
        console.log(`${this.prop1}.foo`);
    }

    bar(){
        console.log(`${this.prop1}.bar`);
    }
}

class SubClass1 extends BaseClass<Type1> {
    constructor(protected dep1: Service1) {
        super(dep1);
        this.prop1 = 'SubClass1';
    }
}

type BaseClassWithoutBar = new <T>(dep1: Service1) => {
    [P in Exclude<keyof BaseClass<T>, 'bar'>]: BaseClass<T>[P];
};

const BaseClassWithoutBar: BaseClassWithoutBar = BaseClass;

class SubClass2 extends BaseClassWithoutBar<Type2> {
    constructor(protected dep1: Service1) {
        super(dep1);
        this.prop1 = 'SubClass2'; // <- Error here
    }

    bar(name: string) {
        console.log(`${this.prop1}.bar -> ${name}`); // <- Error here
    }
}

const sub1: SubClass1 = new SubClass1(new Service1());
const sub2: SubClass2 = new SubClass2(new Service1());

sub1.foo();
sub1.bar();
sub2.foo();
sub2.bar('Bob');

Of course I can get by this e.g. by making the property public or by creating a new method with a different name, but I would still like to know what is actually happening here.

CodePudding user response：

keyof operator does not include private and protected properties.