Dynamic data structures and pointers

Abstract

Array, record and set structures share the common property that they are static. This implies that variables of such a structure maintain the same structure during the whole time of their existence. In many applications, this is an intolerable restriction; they require data which do not only change their value, but also their composition, size, and structure. Typical examples are lists and trees that grow and shrink dynamically. Instead of providing list and tree structures, a collection that for some applications would again not suffice, Modula offers a basic tool to construct arbitrary structures. This is the pointer type.