Programming Perl, 4th Edition

Anonymous Data

In the examples just shown, the backslash operator merely makes a duplicate of a reference that is already held in a variable name—with one exception. The 186_282.42 isn’t referenced by a named variable—it’s just a value. It’s one of those anonymous referents we mentioned earlier. Anonymous referents are accessed only through references. This one happens to be a number, but you can create anonymous arrays, hashes, and subroutines as well.

The anonymous array composer

You can create a reference to an anonymous array with square brackets:

$arrayref = [1, 2, ["a", "b", "c", "d"]];

Here we’ve composed an anonymous array of three elements, whose final element is a reference to an anonymous array of four elements (depicted in Figure 8-2). (The multidimensional syntax described later can be used to access this. For example, $arrayref–>[2][1] would have the value “b”.)

Figure 8-2. A reference to an array, whose third element is itself an array reference

We now have one way to represent the table at the beginning of the chapter:

$table = [ [ "john", 47, "brown", 186],
           [ "mary", 23, "hazel", 128],
           [ "bill", 35, "blue",  157] ];

Square brackets work like this only where the Perl parser is expecting a term in an expression. They should not be confused with the brackets in an expression like $array[6]—although the mnemonic association with arrays is intentional. Inside a quoted string, square ...