Advanced Perl Programming

A View of the Internals

Let us now take a look inside Perl to understand how it manages memory. You can safely skip this section without loss of continuity.

A variable logically represents a binding between a name and a value, as Figure 1.3 illustrates.^[13]

Figure 1-3. A variable is a name and value pair

An array or a hash is not just a collection of numbers or strings. It is a collection of scalar values, and this distinction is important, as Figure 1.4 illustrates.

Figure 1-4. An array value is a collection of scalar values

Each box in Figure 1.4 represents a distinct value. An array has one value that represents the collection of scalar values. Each element of the array is a distinct scalar value. This is analogous to a pride of lions being treated as a single entity (which is why we refer to it in the singular) that has properties distinct from those of the individual lion.

Notice also that while a name always points to a value, a value doesn’t always have to be pointed to by a name, as the array elements in Figure 1.4 or anonymous arrays and hashes exemplify.

Reference Counts

To support painless and transparent memory management, Perl maintains a reference count for every value, whether it is directly pointed to by a name or not. Let’s add this piece of information to our earlier ...