Of course if you put garbage in at the lower levels (e.g. define a monoid instance that doesn't actually commute) then you will get garbage out at the higher levels (e.g. the sum of the concatenation of two lists may no longer equal the two lists' sums added together), but that's not the abstraction leaking, that's just an error in your code.
There are cache-aware abstractions if your situation warrants them. Of course if you abstract over a detail then you lose control over that detail. But that's not the same as a leak, and it's the very essence of programming at all; if the program needs to behave differently every time it runs, then creating a useful program is impossible.
> Or if you have a bad RAM chip.
That's another example of what I said about garbage in, garbage out. The fault isn't in the abstraction, the fault is the bad RAM chip. If you were manually managing all your memory addresses then a bad RAM chip would still present the same problem.
For the record, I meant "Get better theory, and your theory can also talk about the difference between practice and theory."
That abstraction leaks when the actual physical behavior of a RAM chip differs from the abstract specification that it implements.
I find the idea that an abstraction is leaky if different implementations of it perform differently to be fairly useless. I don't think it's a useful concept unless the abstraction captures the expected performance. If the abstraction doesn't give any performance guarantees, then the caller shouldn't have any performance expectations.
Similarly to abstractions around accessing a file on disk that might fail. The abstraction should account for potential failures. If it doesn't account for failures, but the implementation does fail, then it's meaningful to call it leaky.
In fact, this is a common manner for abstractions to become leaky. You find you are in need some guarantee not present in the abstraction. You choose to add whether or not that guarantee is satisfied to the shared interface. Congratulations! You've added a leak to the abstraction.
But that's not the only option available. If you need a guarantee not provided by an abstraction, you could ignore the abstraction and use something that actually provides the guarantees you need.
For example, if I have to care whether the "collection" is implemented as a linked list or as a vector, the the "collection" abstraction has leaked.
I would even argue that's the point of an abstraction. Hide the details that don't matter to the caller. If performance is a detail that matters, and the abstraction doesn't capture it, then you're using the wrong abstraction.
I understood fine. He asserts that "always" on the basis of a handful of examples, only one of which even attempts to show anything more than a performance difference. It's nonsense.
More or less reliability in the datagram layers affects performance - for example, WiFi does its own retransmissions whereas ethernet does not, because WiFi uses a less reliable physical layer, and because you don’t want your packets to have to go from London to New York and back before you discover one of them was lost.
But reliability at the WiFi later cannot give your application the semantics of an ordered data stream, so it is not a substitute for TCP. You can replace TCP with a different transport protocol if you want different behaviour, eg SCTP or DTLS or QUIC, but in all cases they are providing a higher level abstraction than raw datagrams, not just (and not necessarily) more reliability.
2. Bottoms do not make abstractions leaky in some generalised sense. The "fast and loose reasoning is morally correct" result applies: any abstraction that would be valid in a language without bottoms is still valid wherever it evaluates to a non-bottom value.
Of course there's always the thermodynamic argument that "any subprogram has the permanent and externally-detectable side effect of increasing entropy in the universe by converting electricity to heat" but that is to me a bit of a Turing tar-pit of an argument.