TS allow access private class field without error

[terbooter]

TypeScript Version:

$ tsc -v
Version 1.8.10

Create file app.ts with following content:

class User {
    constructor(private name:string) {

    }

    public hello(who:User) {
        // name is the private property of object 'who'. TS should show error like
        // "Cat access private field 'name'"
        console.log("Hello, " + who.name);
    }
}

var vasya = new User("VASYA");
var peter = new User("PETER");
vasya.hello(peter);

Compile this file

tsc app.ts

Actual behavior:
You will see no error.

Expected behavior:
It should show error
"Cat access private field 'name'"

[kitsonk]

BTW, This only occurs when the classes are the same:

class Foo {
    constructor(private name: string) {

    }
}

class User {
    constructor(private name:string) {

    }

    public hello(who: Foo) {
        console.log("Hello, " + who.name); // Property 'name' is private and is only accessible from within class 'Foo'
    }
}

var vasya = new User("VASYA");
var peter = new Foo("PETER");
vasya.hello(peter);

[RyanCavanaugh]

Like in most other languages, classes may access private members of other instances of the same class.

[terbooter]

@RyanCavanaugh could you please give examples of such languages.
Such behaviour is very surprising for me.

[terbooter]

I think name field should be protected to access it from same class
@ahejlsberg said that

Protected members can be accessed only within the declaring class and subclasses of the declaring class.

#688

[kitsonk]

That would still apply... User is the declaring class. The visibility modifiers are at the class level, not the instance level.

@terbooter there is PHP and C# and Java and pretty much every other OO language.

[RyanCavanaugh]

The only language I'm aware of that uses instance-based visibility instead of type-based visibility is Ruby. Java, C#, C++, Swift, PHP, etc. all allow access to other instances' private members.

[terbooter]

Thanks for your answers.