A trivial example of an implicit data structure is an "array data structure", which is an implicit data structure for a list, and requires only the constant overhead of the length; unlike a linked list, which has a pointer associated with each data element, which "explicitly" gives the relationship from one element to the next. Similarly, a "null-terminated string" is an implicit data structure for a string (list of characters). These are considered very simple because they are static data structures (read-only), and only admit the simple operation of iteration over the elements.