A drawback of the pattern collection.with_first(...) is that it requires two definitions of with_first: a non-mutating and a mutating one.
One must be careful when returning a union type.
fun id(_ x: sink Maybe<Int>)) -> Maybe<Int> {
match sink x {
() => { () } // better expressed as `let this: () => { this }`
sink let some => { some }
}
}
Returning () instead of self creates a new existential.
Methods like union or merge require an efficient way to consume the operand.
I wonder whether it's better to define transformations on linked list as conuming or mutating.
Using for_each might be more efficient than iterating over a collection with indices, because we do not need to test bounds at each iteration.
We can't define default implementations of consuming methods. Besides, it's not clear what we need to do in a consuming method to prepare the object's destruction.