Programming Perl, 4th Edition

package

package NAMESPACE VERSION BLOCK
package NAMESPACE VERSION
package NAMESPACE BLOCK
package NAMESPACE

This is not really a function but a declaration that says that the BLOCK, or the rest of the innermost enclosing scope, belongs to the indicated symbol table or namespace. (The scope of a package declaration is thus the same as the scope of a my, state, or our declaration.) Within its scope, the declaration causes the compiler to resolve all unqualified global identifiers by looking them up in the declared package’s symbol table.

A package declaration affects only global variables—including those on which you’ve used local—not lexical variables created with my, state, or our. It only affects unqualified global variables; global variables that are qualified with a package name of their own ignore the current declared package. Global variables declared with our are unqualified and therefore respect the current package, but only at the point of declaration, after which they behave like my variables. That is, for the rest of their lexical scope, our variables are “nailed” to the package in use at the point of declaration, even if a subsequent package declaration intervenes.

Typically, you would put a package declaration as the first thing in a file that is to be included by the require or use operator, but you can put one anywhere a statement would be legal. When creating a traditional or object-oriented module file, it is customary to name the package the same name as the file to ...