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The Semantics of Arrays

The arrays in Perl are semantically closest to lists in Lisp or Scheme (sans cons cells), however the syntax that is used to access arrays is closer to arrays in C. In fact, one can often treat Perl's arrays as if they were simply C arrays, but they are actually much more powerful than that.

Perl arrays grow and shrink dynamically as needed. The more data you put into a Perl list, the bigger it gets. As you remove elements from the list, the list will shrink to the right size. Note that this is inherently different from arrays in the C language, where the programmer must keep track and control the size of the array.

However, Perl arrays are accessible just like C arrays. So, you can subscript to anywhere within a given list at will. There is no need to process through the first four elements of the list to get the fifth element (as in Scheme). In this manner, you get the advantages of both a dynamic list, and a static-size array.

The only penalty that you pay for this flexibility is that when an array is growing very large very quickly, it can be a bit inefficient. However, when this must occur, Perl allows you to pre-build an array of certain size. We will show how to do this a bit later.

A Perl array is always a list of scalars. Of course, since Perl makes no direct distinction between numeric and string values, you can easily mix different types of scalars within the same array. However, everything in the array must be a scalar1.

Note the difference in terminology that is used here. Arrays refer to variables that store a list of scalar values. Lists can be written as literals (see List Literals) and used in a variety of ways. One of the ways that list literals can be used is to assign to array variables (see Array Variables). We will discuss both list literals and array variables in this chapter.


  1. It is possible to make an array of arrays using a concept called ``references'', but that topic is beyond the scope of this book.