state

#!/usr/bin/perl -w
#
use strict;

my @name;

&greet("jo");
&greet("hu");
&greet("liu");

sub greet{
    my ($str) = @_;
    if(not @name){
        print "Hi $str! You are the firest on here!\n";
    }else{
        print "Hi $str! $name[-1] is also here!\n";
    }
    push @name, $str;
}

Hi jo! You are the firest on here!
Hi hu! jo is also here!
Hi liu! hu is also here!

use state

use 5.010;
greet( 'Fred' );
greet( 'Barney' );
greet( 'Wilma' );
greet( 'Betty' );
sub greet {
    state @names;
    my $name = shift;
    print "Hi $name! ";
    if( @names ) {
        print "I've seen: @names\n";
        }
    else {
        print "You are the first one here!\n";
        }
    push @names, $name;
    }

state EXPR

• state TYPE EXPR
• state EXPR : ATTRS
• state TYPE EXPR : ATTRS

  declares a lexically scoped variable, just like does. However, those variables will never be reinitialized, contrary to lexical variables that are reinitialized each time their enclosing block is entered.

  variables are enabled only when the feature "state" pragma is in effect. See .

There’s a slight restriction on arrays and hashes as state variables, though. We can’t
initialize them in list context as of Perl 5.10:
state @array = qw(a b c); # Error!