Many useful classes operate as containers of elements. Techniques for accessing these elements from a container differ from class to class. A Pix acts in some ways like an index, and in some ways like a pointer. In virtually all cases, Pixes are pointers to some kind internal storage cells. The containers use these pointers to extract items.
Pixes support traversal and inspection of elements in a collection using analogs of array indexing.
However, they are pointer-like in that 0 is treated as an invalid Pix , and unsafe insofar as programmers can attempt to access nonexistent elements via dangling or otherwise invalid Pixes without first checking for their validity. In general it is a very bad idea to perform traversals in the the midst of destructive modifications to containers. Classes supporting the use of Pixes always contain the following methods, assuming a container a of element types of Base . This is often a relatively slow operation, since the collection must usually traverse through elements to see if any correspond to the Pix. Go to the previous , next section.