Packages and explicit public interfaces

The idea

A package supplies a namespace for named subroutines and package variables. It does not replace lexical scoping: my still creates lexical variables, while our declares access to a package variable under strict checking. Qualified names make the owning namespace visible, helping a reader distinguish unrelated helpers that happen to use the same short name.

A module usually places reusable code in a file that can be loaded and may export a deliberate set of names. Export only the operations that form the public interface rather than flooding a caller’s namespace. Loading, importing, and runtime invocation are different events; use performs its load and import during compilation. Keep initialization predictable and avoid depending on accidental caller globals.

use strict; use warnings;
{ package Metrics; sub double { my ($n)=@_; return $n*2; } }
print Metrics::double(6),"\n";

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The qualified call names the package owning double, avoiding any need to import an unqualified helper.