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Challengewhat does this code print?
time to read 1 min | 42 words
Given the following code:
Can you guess what it will do?
Can you explain why?
I love that this snippet is under 20 lines of code, but being able to explain it shows a lot more knowledge about C# than you would expect.
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Comments
Iterator is a struct so when you access the
Valueproperty it will copy the value onto the stack and use it locally, so when you callit.Value.MoveNext()the method call is going to a new copy. Same is true when you callit.Value.Current... you are dealing with a new instance again. Code will loop forever printing0. Since the copy happens on read, it doesn't even matter that you are usingNullable<Iterator>here (also a struct), the same behavior happens even if you had a reference type boxing the value and passed that around.I should clarify that using
Nullable<Iterator>(akaIterator?) is how you force the copy-by-value behavior here because you no longer are pointing directly to the value on the stack, you'll always be getting a copy.It prints 0 forever. Every time you call
it.Value, you get a new copy of the struct, so the struct actually contained in the nullable never changes.It will give you infinite stream of zeros. Is there a reason why one might need to use Nullable<Iterator> here ? I mean - it's clear that it will always give you a copy of value thus being a culprit of this "unusual" behaviour. But why one might want to try it ?
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