stream | driven readable and writable streams | Runtime Evironment library

This worked well for me in .Net 5.
Now I wanted to update my project to .Net 6.

When using .Net 6, the decrypted string does get cut off a certain point depending on the length of the input string.

▶️ To make it easy to debug/reproduce my issue, I created a public repro Repository here.

• The encryption code is on purpose in a Standard 2.0 Project.
• Referencing this project are both a .Net 6 as well as a .Net 5 Console project.

Both are calling the encryption methods with the exact same input of "12345678901234567890" with the path phrase of "nzv86ri4H2qYHqc&m6rL".

.Net 5 output: "12345678901234567890"
.Net 6 output: "1234567890123456"

The difference in length is 4.

I also looked at the breaking changes for .Net 6, but could not find something which guided me to a solution.

I'm glad for any suggestions regarding my issue, thanks!

Encryption Class

Consider the "category of types", something like Hask but with whatever adjustment that fits the discussion. Within such a category, it is said that (1) the initial algebras define datatypes, and (2) terminal algebras define codatatypes.

I'm struggling to convince myself of (2).

Consider the functor T(t) = 1 + a * t. I agree that the initial T-algebra is well-defined and indeed defines [a], the list of a. By definition, the initial T-algebra is a type X together with a function f :: 1+a*X -> X, such that for any other type Y and function g :: 1+a*Y -> Y, there is exactly one function m :: X -> Y such that m . f = g . T(m) (where . denotes the function combination operator as in Haskell). With f interpreted as the list constructor(s), g the initial value and the step function, and T(m) the recursion operation, the equation essentially asserts the unique existance of the function m given any initial value and any step function defined in g, which necessitates an underlying well-behaved fold together with the underlying type, the list of a.

For example, g :: Unit + (a, Nat) -> Nat could be () -> 0 | (_,n) -> n+1, in which case m defines the length function, or g could be () -> 0 | (_,n) -> 0, then m defines a constant zero function. An important fact here is that, for whatever g, m can always be uniquely defined, just as fold does not impose any contraint on its arguments and always produce a unique well-defined result.

This does not seem to hold for terminal algebras.

Consider the same functor T defined above. The definition of the terminal T-algebra is the same as the initial one, except that m is now of type X -> Y and the equation now becomes m . g = f . T(m). It is said that this should define a potentially infinite list.

I agree that this is sometimes true. For example, when g :: Unit + (Unit, Int) -> Int is defined as () -> 0 | (_,n) -> n+1 like before, m then behaves such that m(0) = () and m(n+1) = Cons () m(n). For non-negative n, m(n) should be a finite list of units. For any negative n, m(n) should be of infinite length. It can be verified that the equation above holds for such g and m.

With any of the two following modified definition of g, however, I don't see any well-defined m anymore.

First, when g is again () -> 0 | (_,n) -> n+1 but is of type g :: Unit + (Bool, Int) -> Int, m must satisfy that m(g((b,i))) = Cons b m(g(i)), which means that the result depends on b. But this is impossible, because m(g((b,i))) is really just m(i+1) which has no mentioning of b whatsoever, so the equation is not well-defined.

Second, when g is again of type g :: Unit + (Unit, Int) -> Int but is defined as the constant zero function g _ = 0, m must satisfy that m(g(())) = Nil and m(g(((),i))) = Cons () m(g(i)), which are contradictory because their left hand sides are the same, both being m(0), while the right hand sides are never the same.

In summary, there are T-algebras that have no morphism into the supposed terminal T-algebra, which implies that the terminal T-algebra does not exist. The theoretical modeling of the codatatype Stream (or infinite list), if any, cannot be based on the nonexistant terminal algebra of the functor T(t) = 1 + a * t.

Many thanks to any hint of any flaw in the story above.

Live supplies (that is, the types that come from a Supplier and get new values whenever that Supplier emits a value) make sense to me – they're a version of asynchronous streams that I can use to broadcast a message from one or more senders to one or more receivers. It's easy to see use cases for responding to a live stream of messages: I might want to take an action every time I get a UI event from a GUI interface, or every time a chat application broadcasts that it has received a new message.

But on-demand supplies don't make a similar amount of sense. The docs say that

An on-demand broadcast is like Netflix: everyone who starts streaming a movie (taps a supply), always starts it from the beginning (gets all the values), regardless of how many people are watching it right now.

Ok, fair enough. But why/when would I want those semantics?

The examples also leave me scratching my head a bit. The Concurancy page currently provides three examples of a supply block, but two of them just emit the values from a for loop. The third is a bit more detailed: