Demonstration of the use of a state variable in a Mojolicious app

state.pl

#!/usr/bin/env perl
package A;
use Mojo::Base -base;

  use 5.020;
  use feature qw(signatures);

  has [qw(a b)];

  sub new {
    my $self = shift->SUPER::new(@_);
    warn 'new';
    $self;
  }
  sub c ($self) { $self->a + $self->b }

package main;
use Mojolicious::Lite;

  helper a => sub { warn 'a'; A->new(a => $_[1], b => $_[2]) }; # Always re-call A->new
  helper b => sub { warn 'b'; state $a = A->new(a => $_[1], b => $_[2]) }; # if state $variable is already set, just it and don't use it again.  Or:
  helper c => sub { warn 'c'; shift->{_state} ||= A->new(a => $_[0], b => $_[1]) }; # b & c are equivalent

  get '/' => sub {
    my $c = shift;
    warn "!! A\n";
    warn $c->a(1,2)->c; # 3
    warn $c->a(2,3)->c; # 5 (NOTE!)
    warn "!! B\n";
    warn $c->b(3,4)->c; # 7
    warn $c->b(4,5)->c; # 7
    warn "!! C\n";
    warn $c->c(5,6)->c; # 11
    warn $c->c(6,7)->c; # 11
    $c->render(text => scalar localtime);
  };

  app->start;

__END__
!! A
a at state.pl line 20.
new at state.pl line 12.
3 at state.pl line 27.
a at state.pl line 20.
new at state.pl line 12.
5 at state.pl line 28.
!! B
b at state.pl line 21.
new at state.pl line 12.
7 at state.pl line 30.
b at state.pl line 21.
7 at state.pl line 31.
!! C
c at state.pl line 22.
new at state.pl line 12.
11 at state.pl line 33.
c at state.pl line 22.
11 at state.pl line 34.