home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Skunkware 5
/
Skunkware 5.iso
/
man
/
cat.1
/
perlbot.1
< prev
next >
Wrap
Text File
|
1995-07-25
|
17KB
|
529 lines
PPPPEEEERRRRLLLLBBBBOOOOTTTT((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((RRRReeeelllleeeeaaaasssseeee 0000....0000 PPPPaaaattttcccchhhhlllleeeevvvveeeellll 00000000)))) PPPPEEEERRRRLLLLBBBBOOOOTTTT((((1111))))
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";
Page 1 (printed 6/30/95)
PPPPEEEERRRRLLLLBBBBOOOOTTTT((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((RRRReeeelllleeeeaaaasssseeee 0000....0000 PPPPaaaattttcccchhhhlllleeeevvvveeeellll 00000000)))) PPPPEEEERRRRLLLLBBBBOOOOTTTT((((1111))))
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.
Page 2 (printed 6/30/95)
PPPPEEEERRRRLLLLBBBBOOOOTTTT((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((RRRReeeelllleeeeaaaasssseeee 0000....0000 PPPPaaaattttcccchhhhlllleeeevvvveeeellll 00000000)))) PPPPEEEERRRRLLLLBBBBOOOOTTTT((((1111))))
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.
Page 3 (printed 6/30/95)
PPPPEEEERRRRLLLLBBBBOOOOTTTT((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((RRRReeeelllleeeeaaaasssseeee 0000....0000 PPPPaaaattttcccchhhhlllleeeevvvveeeellll 00000000)))) PPPPEEEERRRRLLLLBBBBOOOOTTTT((((1111))))
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;
Page 4 (printed 6/30/95)
PPPPEEEERRRRLLLLBBBBOOOOTTTT((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((RRRReeeelllleeeeaaaasssseeee 0000....0000 PPPPaaaattttcccchhhhlllleeeevvvveeeellll 00000000)))) PPPPEEEERRRRLLLLBBBBOOOOTTTT((((1111))))
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;
Page 5 (printed 6/30/95)
PPPPEEEERRRRLLLLBBBBOOOOTTTT((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((RRRReeeelllleeeeaaaasssseeee 0000....0000 PPPPaaaattttcccchhhhlllleeeevvvveeeellll 00000000)))) PPPPEEEERRRRLLLLBBBBOOOOTTTT((((1111))))
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;
}
Page 6 (printed 6/30/95)
PPPPEEEERRRRLLLLBBBBOOOOTTTT((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((RRRReeeelllleeeeaaaasssseeee 0000....0000 PPPPaaaattttcccchhhhlllleeeevvvveeeellll 00000000)))) PPPPEEEERRRRLLLLBBBBOOOOTTTT((((1111))))
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;
}
Page 7 (printed 6/30/95)
PPPPEEEERRRRLLLLBBBBOOOOTTTT((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((RRRReeeelllleeeeaaaasssseeee 0000....0000 PPPPaaaattttcccchhhhlllleeeevvvveeeellll 00000000)))) PPPPEEEERRRRLLLLBBBBOOOOTTTT((((1111))))
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;
Page 8 (printed 6/30/95)
