Skunkware 5/Skunkware 5.iso/man/cat.1/perlbot.1

Text File | 1995-07-26 | 16.7 KB | 529 lines

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     NNNNAAAAMMMMEEEE
          perlbot - Bag'o Object Tricks For Perl5 (the BOT)

     IIIINNNNTTTTRRRROOOODDDDUUUUCCCCTTTTIIIIOOOONNNN
          The following collection of tricks and hints is intended to
          whet curious appetites about such things as the use of
          instance variables and the mechanics of object and class
          relationships.  The reader is encouraged to consult relevant
          textbooks for discussion of Object Oriented definitions and
          methodology.  This is not intended as a comprehensive guide
          to Perl5's object oriented features, nor should it be
          construed as a style guide.

          The Perl motto still holds:  There's more than one way to do
          it.

     IIIINNNNSSSSTTTTAAAANNNNCCCCEEEE VVVVAAAARRRRIIIIAAAABBBBLLLLEEEESSSS
          An anonymous array or anonymous hash can be used to hold
          instance variables.  Named parameters are also demonstrated.

                  package Foo;

                  sub new {
                          my $type = shift;
                          my %params = @_;
                          my $self = {};
                          $self->{'High'} = $params{'High'};
                          $self->{'Low'}  = $params{'Low'};
                          bless $self;
                  }

                  package Bar;

                  sub new {
                          my $type = shift;
                          my %params = @_;
                          my $self = [];
                          $self->[0] = $params{'Left'};
                          $self->[1] = $params{'Right'};
                          bless $self;
                  }

                  package main;

                  $a = new Foo ( 'High' => 42, 'Low' => 11 );
                  print "High=$a->{'High'}\n";
                  print "Low=$a->{'Low'}\n";

                  $b = new Bar ( 'Left' => 78, 'Right' => 40 );
                  print "Left=$b->[0]\n";
                  print "Right=$b->[1]\n";




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     SSSSCCCCAAAALLLLAAAARRRR IIIINNNNSSSSTTTTAAAANNNNCCCCEEEE VVVVAAAARRRRIIIIAAAABBBBLLLLEEEESSSS
          An anonymous scalar can be used when only one instance
          variable is needed.

                  package Foo;

                  sub new {
                          my $type = shift;
                          my $self;
                          $self = shift;
                          bless \$self;
                  }

                  package main;

                  $a = new Foo 42;
                  print "a=$$a\n";


     IIIINNNNSSSSTTTTAAAANNNNCCCCEEEE VVVVAAAARRRRIIIIAAAABBBBLLLLEEEE IIIINNNNHHHHEEEERRRRIIIITTTTAAAANNNNCCCCEEEE
          This example demonstrates how one might inherit instance
          variables from a superclass for inclusion in the new class.
          This requires calling the superclass's constructor and
          adding one's own instance variables to the new object.

                  package Bar;

                  sub new {
                          my $self = {};
                          $self->{'buz'} = 42;
                          bless $self;
                  }

                  package Foo;
                  @ISA = qw( Bar );

                  sub new {
                          my $self = new Bar;
                          $self->{'biz'} = 11;
                          bless $self;
                  }

                  package main;

                  $a = new Foo;
                  print "buz = ", $a->{'buz'}, "\n";
                  print "biz = ", $a->{'biz'}, "\n";


     OOOOBBBBJJJJEEEECCCCTTTT RRRREEEELLLLAAAATTTTIIIIOOOONNNNSSSSHHHHIIIIPPPPSSSS
          The following demonstrates how one might implement
          "containing" and "using" relationships between objects.



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                  package Bar;

                  sub new {
                          my $self = {};
                          $self->{'buz'} = 42;
                          bless $self;
                  }

                  package Foo;

                  sub new {
                          my $self = {};
                          $self->{'Bar'} = new Bar ();
                          $self->{'biz'} = 11;
                          bless $self;
                  }

                  package main;

                  $a = new Foo;
                  print "buz = ", $a->{'Bar'}->{'buz'}, "\n";
                  print "biz = ", $a->{'biz'}, "\n";


     OOOOVVVVEEEERRRRRRRRIIIIDDDDIIIINNNNGGGG SSSSUUUUPPPPEEEERRRRCCCCLLLLAAAASSSSSSSS MMMMEEEETTTTHHHHOOOODDDDSSSS
          The following example demonstrates how one might override a
          superclass method and then call the method after it has been
          overridden.  The Foo::Inherit class allows the programmer to
          call an overridden superclass method without actually
          knowing where that method is defined.

                  package Buz;
                  sub goo { print "here's the goo\n" }

                  package Bar; @ISA = qw( Buz );
                  sub google { print "google here\n" }

                  package Baz;
                  sub mumble { print "mumbling\n" }

                  package Foo;
                  @ISA = qw( Bar Baz );
                  @Foo::Inherit::ISA = @ISA;  # Access to overridden methods.












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                  sub new { bless [] }
                  sub grr { print "grumble\n" }
                  sub goo {
                          my $self = shift;
                          $self->Foo::Inherit::goo();
                  }
                  sub mumble {
                          my $self = shift;
                          $self->Foo::Inherit::mumble();
                  }
                  sub google {
                          my $self = shift;
                          $self->Foo::Inherit::google();
                  }

                  package main;

                  $foo = new Foo;
                  $foo->mumble;
                  $foo->grr;
                  $foo->goo;
                  $foo->google;


     UUUUSSSSIIIINNNNGGGG RRRREEEELLLLAAAATTTTIIIIOOOONNNNSSSSHHHHIIIIPPPP WWWWIIIITTTTHHHH SSSSDDDDBBBBMMMM
          This example demonstrates an interface for the SDBM class.
          This creates a "using" relationship between the SDBM class
          and the new class Mydbm.

                  use SDBM_File;
                  use POSIX;

                  package Mydbm;






















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                  sub TIEHASH {
                      my $self = shift;
                      my $ref  = SDBM_File->new(@_);
                      bless {'dbm' => $ref};
                  }
                  sub FETCH {
                      my $self = shift;
                      my $ref  = $self->{'dbm'};
                      $ref->FETCH(@_);
                  }
                  sub STORE {
                      my $self = shift;
                      if (defined $_[0]){
                          my $ref = $self->{'dbm'};
                          $ref->STORE(@_);
                      } else {
                          die "Cannot STORE an undefined key in Mydbm\n";
                      }
                  }

                  package main;

                  tie %foo, Mydbm, "Sdbm", O_RDWR|O_CREAT, 0640;
                  $foo{'bar'} = 123;
                  print "foo-bar = $foo{'bar'}\n";

                  tie %bar, Mydbm, "Sdbm2", O_RDWR|O_CREAT, 0640;
                  $bar{'Cathy'} = 456;
                  print "bar-Cathy = $bar{'Cathy'}\n";


     TTTTHHHHIIIINNNNKKKKIIIINNNNGGGG OOOOFFFF CCCCOOOODDDDEEEE RRRREEEEUUUUSSSSEEEE
          One strength of Object-Oriented languages is the ease with
          which old code can use new code.  The following examples
          will demonstrate first how one can hinder code reuse and
          then how one can promote code reuse.

          This first example illustrates a class which uses a fully-
          qualified method call to access the "private" method _B_A_Z().
          The second example will show that it is impossible to
          override the _B_A_Z() method.

                  package FOO;

                  sub new { bless {} }
                  sub bar {
                          my $self = shift;
                          $self->FOO::private::BAZ;
                  }

                  package FOO::private;




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                  sub BAZ {
                          print "in BAZ\n";
                  }

                  package main;

                  $a = FOO->new;
                  $a->bar;

          Now we try to override the _B_A_Z() method.  We would like
          _F_O_O::_b_a_r() to call _G_O_O_P::_B_A_Z(), but this cannot happen since
          _F_O_O::_b_a_r() explicitly calls _F_O_O::_p_r_i_v_a_t_e::_B_A_Z().

                  package FOO;

                  sub new { bless {} }
                  sub bar {
                          my $self = shift;
                          $self->FOO::private::BAZ;
                  }

                  package FOO::private;

                  sub BAZ {
                          print "in BAZ\n";
                  }

                  package GOOP;
                  @ISA = qw( FOO );
                  sub new { bless {} }

                  sub BAZ {
                          print "in GOOP::BAZ\n";
                  }

                  package main;

                  $a = GOOP->new;
                  $a->bar;

          To create reusable code we must modify class FOO, flattening
          class FOO::private.  The next example shows a reusable class
          FOO which allows the method _G_O_O_P::_B_A_Z() to be used in place
          of _F_O_O::_B_A_Z().

                  package FOO;

                  sub new { bless {} }
                  sub bar {
                          my $self = shift;
                          $self->BAZ;
                  }



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                  sub BAZ {
                          print "in BAZ\n";
                  }

                  package GOOP;
                  @ISA = qw( FOO );

                  sub new { bless {} }
                  sub BAZ {
                          print "in GOOP::BAZ\n";
                  }

                  package main;

                  $a = GOOP->new;
                  $a->bar;


     CCCCLLLLAAAASSSSSSSS CCCCOOOONNNNTTTTEEEEXXXXTTTT AAAANNNNDDDD TTTTHHHHEEEE OOOOBBBBJJJJEEEECCCCTTTT
          Use the object to solve package and class context problems.
          Everything a method needs should be available via the object
          or should be passed as a parameter to the method.

          A class will sometimes have static or global data to be used
          by the methods.  A subclass may want to override that data
          and replace it with new data.  When this happens the
          superclass may not know how to find the new copy of the
          data.

          This problem can be solved by using the object to define the
          context of the method.  Let the method look in the object
          for a reference to the data.  The alternative is to force
          the method to go hunting for the data ("Is it in my class,
          or in a subclass?  Which subclass?"), and this can be
          inconvenient and will lead to hackery.  It is better to just
          let the object tell the method where that data is located.

                  package Bar;

                  %fizzle = ( 'Password' => 'XYZZY' );

                  sub new {
                          my $self = {};
                          $self->{'fizzle'} = \%fizzle;
                          bless $self;
                  }









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                  sub enter {
                          my $self = shift;

                          # Don't try to guess if we should use %Bar::fizzle
                          # or %Foo::fizzle.  The object already knows which
                          # we should use, so just ask it.
                          #
                          my $fizzle = $self->{'fizzle'};

                          print "The word is ", $fizzle->{'Password'}, "\n";
                  }

                  package Foo;
                  @ISA = qw( Bar );

                  %fizzle = ( 'Password' => 'Rumple' );

                  sub new {
                          my $self = Bar->new;
                          $self->{'fizzle'} = \%fizzle;
                          bless $self;
                  }

                  package main;

                  $a = Bar->new;
                  $b = Foo->new;
                  $a->enter;
                  $b->enter;


























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