I’ve only ever seen “one-time” in cryptography to refer to One-Time Pads (OTP). They are literally uncrackable (because every possible plaintext could be encoded by every possible ciphertext) but they achieve that by using a shared private key. The cipher becomes attackable if the key is re-used, hence the “one-time.”
But that key has to be exchanged somehow, and that exchange can be attacked instead. Key exchange algorithms can’t necessarily transfer every possible OTP which means eavesdropping on the exchange would make an OTP attackable. So the best option we know of that doesn’t require secret meetings to share OTPs* really is to use RSA encryption. Once we have efficient quantum-resistant schemes, they’ll be the best option we know.
* and let’s be honest, secret meetings can be eavesdropped on as well.
“Monadic type” has something like three meanings depending on context, and it’s not clear which one you mean. One of them is common in math, but not so common in programming, so probably not that. But neither “parametric types with a single argument” nor “types that encode a category-theoretic monad” have the property you say, as far as I know.
I imagine you’re probably referring to the latter, since the optional monad exists. That’s very different from returning null. The inhabitants of
Integer
in Java, for example, are the boxed machine ints andnull
. The inhabitants ofOptional[Integer]
(it won’t let me use angle brackets here) areOptional.of(i)
for each machine inti
,Optional.empty()
, andnull
.Optional.empty()
is not null and should not be called a “Null object.” It’s also not of typeInteger
, so you’re not even allowed to return it unless the function type explicitly says so. Writing such function types is pretty uncommon to do in java programs but it’s more normal in kotlin. In languages like Haskell, which don’t havenull
at all, this is idiomatic.