my declares a lexically scoped variable. A lexical scope continues until the closing brace (}) that ends the block it was defined in, or until the end of the file, whichever comes first.

{
  package Foo;
  my $foo = 1;
  package Bar;
  # can still see $foo here
  package Baz;
  # can still see $foo here
}
# cannot see $foo any more

[download]

While our variables are associated with a particular package, they too are lexically scoped:

{
  package Foo;
  our $foo = 1; # $foo is an alias for $Foo::foo
  package Bar;
  # $foo is still an alias for $Foo::foo here
  package Baz;
  # $foo is still an alias for $Foo::foo here
}
# cannot see $foo any more

[download]

For this reason, if you're defining multiple packages in the same file, it's a good idea to define them each within their own {...} block, so they don't accidentally leak variables. (Of course, sometimes - probably quite rarely - you'll actually want to share a lexical variable between the packages, in which case, just declare it right at the top before the first opening brace.)

package Cow { use Moo; has name => (is => 'lazy', default => sub { 'Mooington' }) } say Cow->new->name

In reply to Re: my $var masked across package scope? by tobyink
in thread my $var masked across package scope? by QM

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