After more than a year since the previous instalment...
A C# method that returns an enumerator via
yield return generates a synthetic class that looks like this:
where I omit unimportant detail based on the particular enumeration, but draw attention to how the other
IEnumerator methods are implemented.
The F# result from a sequence expression is very different, with an explicit close and dispose:
GeneratedSequenceBase we have
Close method renders the enumeration non-functional, though the closed enumerator does not throw, it simply yields no more. That the resulting sequence has an active
Dispose behaviour, unlike the C# case, explains why in the
Window example I needed to add the
Controlled wrapper to block that, so that the
Stream based enumeration written as a sequence expression would draw more than one tranche before stopping.
By contrast, you don't need the
Controlled wrapper for windowing the BCL derived array-as-enumerator; presumably that has a no-op