* if an item is streamable, its value will be retrieved, and a new item containing the value will be returned.
* other, non-streamable items will simply be passed through.
Materialization is helpful if a value is to be processed more than once. It is even mandatory if the value needs to be retrieved before other actionstake place that invalidate the resource, such as the a deletion of a resource, take placean addressed file.
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| '''Example'''