[fodkodrasz]

> OK. Or just declare your parameter as IEnumerable<>? This has the effect of restricting the operations on the incoming collection in the same way.

It does not work that way, because it is an `in` parameter, thus you can still accept any mutable type (including an array) which implements the essentially immutable IEnumerable interface you require.

Now if it was about a return value, it would be a different story.

edit:

Still what you suggest has its merits in the other direction, as it gives the caller a guarantee that the passed in collection will not be modified inside. Had to untangle broken code (without unit test when i got it) that was called like something `CalculateCost(SomegraphData input)` and while its name (and xmldoc) did not suggest, it did subtle modification to the data it got handed in... I was very upset about that legacy codebase I just inherited when I found that...