Our local state, my, my - Understanding Perl variables

Our local state, my, my

Your speaker for the evening

● Sawyer X● Github.com/xsawyerx● Blogs.perl.org/users/sawyer_x● #dancer @ irc.perl.org

Our local state, my, my

our, local, state, my, my

Perl variables, the easy part

● our is global● my is lexical

Easy part done!

What's a global variable?

● Perl code is divided to namespaces● We use 'package' to declare them● 'main' is the default namespace● Globals are package variables● Variables relating to that namespace● (not the same as “superglobals”)● (globals are saved in typeglobs)

Global variables, examples

● our $name; # $main::name

● package My::Package;

our $name; # $My::Package::name

● say $Moose::VERSION;

Globals: done!

What's a lexical variable?

● Scoped variables● Variables that exist only in a scope!● Available scopes: block, file, eval● We define lexical variables with 'my' ● (they are saved in a lex pad)

Lexical variables, examples

● { my $exists_only_here }● { my $outer; { my $inner } }● foreach my $name (@names) {

say $name; # okay

}

say $name; # error

Lexical variables, pop quiz!

package Example;

my $exvar = 30;

package main;

say $exvar;

● Error or no error?

Lexical variables, pop quiz!

● No error!● my is lexical● package is a namespace, not a scope● The scope here is the “file scope”● Here is the correct way to do it:

{ package Example; my $exvar; }

Lexicals: done!

What's a state variable?

● Lexical variables with a twist!● They don't get reinitialized● sub inc {

state $myvar = 0; # default value

return ++$myvar;

}

say inc($_) for 1 .. 10;

States: Done!

What's a local variable?

● Something that confuses people● But very simple, actually● Localizes an already existing variable● Used to temporarily override

variables instead of creating new ones● Useful with superglobals● Prevents fscking them up

Local variables, examples

● Slurping file content:

use autodie;

open my $fh, '<', $filename;

my $content = do { local $/; <$fh> };

close $fh;

Local variables, examples

● No output buffering for this scope:

local $| = 1;● Disabling warnings for a scope:

{

local $^W = 0;

# do something that would warn

}

Locals: done!

Questions?

Thank you!(yes, you can finally go home)