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by rbehrends 2803 days ago
> This is a thing people say, but I think it's misleading. Reference counting can increase the lifetime of an object, but borrowing cannot. I've seen this really trip up beginners.

"With a maximum reference count of 1." As the reference count becomes 1 upon object creation, it cannot really be increased further. Hence, only operations that keep the (virtual) reference count at 1 or reduce it to 0 are allowed.

My point here is that you inherently cannot do things where you cannot prove that this virtual reference count can be capped at 1.
1 comments
steveklabnik 2803 days ago
That doesn't change much; the point is that (in many languages), variables going into or out of scopes don't fiddle with the ref count[1], and so people assume that something will live until they make the count go down explicitly.

It also only refers to ownership, not borrowing, and both are equally important.

Beyond that, what I'm saying is something more meta: It doesn't really matter if this analogy is spot-on or not; it's got enough wiggle room in it that I've seen it trip up beginners. Maybe that's because they misunderstand the analogy, but given that its point is to convey understanding, that means that it isn't a great analogy, in my experience. YMMV.

1: directly, of course; this also depends on the language.

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rbehrends 2803 days ago
> It also only refers to ownership, not borrowing, and both are equally important.

I addressed borrowing above. Borrowing is proving lifetime subset properties and that you therefore can avoid increasing the virtual reference count.

And this is not about whether this is useful for beginners. It is to illustrate inherent limitations of the approach.

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steveklabnik 2803 days ago
> I addressed borrowing above. Borrowing is proving lifetime subset properties and that

Right, so what I'm saying is, the description of borrowing doesn't really fit in with the reference counting aspect of the analogy, so it ends up being separate from it.

> And this is not about whether this is useful for beginners.

Right, that was my point. :)

I mean, in the end, do what you'd like. All I'm saying is that I've seen this analogy lead to tons of confusion. YMMV.

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