[kannanvijayan]

> The same is true of a piece of code that writes through the reference or returns it. That's how sub-typing works.

But it is not true that it is correctly typed with respect to a a supertype of A (it is not valid to call the code with a reference to a supertype of A).

Code that only writes through the reference is correctly typed with respect to a super-type of A (it is valid to call the code with a reference to a supertype of A).

> Have you ever programmed in a language with subtyping?

Sigh, keep that snark for the twitter battles. I don't care enough about this to get snippy about it or to deal with folks who do.

[James_K]

> Code that only writes through the reference is correctly typed with respect to a super-type of A (it is valid to call the code with a reference to a supertype of A).

I'm not trying to be snarky, I genuinely want to know what you think of that code snippet I showed you. You claim it should work, but anyone with an understanding of programming would tell you it shouldn't. You can't write to a member variable that doesn't exist. Have you encountered inheritance before? Do you know what a “super-type” is? The mistake you're making here is very basic and I should like to know your level of experience.