operator
item of shelf-name indexer?
When it is known that a shelf has a specific key, it is possible to find which item has that key with the item of
operator.
This operation gives the position of the specified item on the shelf. It is an error if the specified item does not exist. One way to avoid this error when selecting an item by its key is to guarantee that the shelf has the key before looking for its position (the has key
test can be used to do this).