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视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

\&
\&        package Foo;
\&        @ISA = qw( Bar Baz );
\&
\&        sub new {
\&                my $type = shift;
\&                bless [], $type;
\&        }
\&        sub grr { print "grumble\en" }
\&        sub goo {
\&                my $self = shift;
\&                $self\->SUPER::goo();
\&        }
\&        sub mumble {
\&                my $self = shift;
\&                $self\->SUPER::mumble();
\&        }
\&        sub google {
\&                my $self = shift;
\&                $self\->SUPER::google();
\&        }
\&
\&        package main;
\&
\&        $foo = Foo\->new;
\&        $foo\->mumble;
\&        $foo\->grr;
\&        $foo\->goo;
\&        $foo\->google;
.Ve
.PP
Note that \f(CW\*(C`SUPER\*(C'\fR refers to the superclasses of the current package
(\f(CW\*(C`Foo\*(C'\fR), not to the superclasses of \f(CW$self\fR.
.SH "USING RELATIONSHIP WITH SDBM"
.IX Header "USING RELATIONSHIP WITH SDBM"
This example demonstrates an interface for the \s-1SDBM\s0 class.  This creates a
\&\*(L"using\*(R" relationship between the \s-1SDBM\s0 class and the new class Mydbm.
.PP
.Vb 1
\&        package Mydbm;
\&
\&        require SDBM_File;
\&        require Tie::Hash;
\&        @ISA = qw( Tie::Hash );
\&
\&        sub TIEHASH {
\&            my $type = shift;
\&            my $ref  = SDBM_File\->new(@_);
\&            bless {\*(Aqdbm\*(Aq => $ref}, $type;
\&        }
\&        sub FETCH {
\&            my $self = shift;
\&            my $ref  = $self\->{\*(Aqdbm\*(Aq};
\&            $ref\->FETCH(@_);
\&        }
\&        sub STORE {
\&            my $self = shift;
\&            if (defined $_[0]){
\&                my $ref = $self\->{\*(Aqdbm\*(Aq};
\&                $ref\->STORE(@_);
\&            } else {
\&                die "Cannot STORE an undefined key in Mydbm\en";
\&            }
\&        }
\&
\&        package main;
\&        use Fcntl qw( O_RDWR O_CREAT );
\&
\&        tie %foo, "Mydbm", "Sdbm", O_RDWR|O_CREAT, 0640;
\&        $foo{\*(Aqbar\*(Aq} = 123;
\&        print "foo\-bar = $foo{\*(Aqbar\*(Aq}\en";
\&
\&        tie %bar, "Mydbm", "Sdbm2", O_RDWR|O_CREAT, 0640;
\&        $bar{\*(AqCathy\*(Aq} = 456;
\&        print "bar\-Cathy = $bar{\*(AqCathy\*(Aq}\en";
.Ve
.SH "THINKING OF CODE REUSE"
.IX Header "THINKING OF CODE REUSE"
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.
.PP
This first example illustrates a class which uses a fully-qualified method
call to access the \*(L"private\*(R" method \s-1\fIBAZ\s0()\fR.  The second example will show
that it is impossible to override the \s-1\fIBAZ\s0()\fR method.
.PP
.Vb 1
\&        package FOO;
\&
\&        sub new {
\&                my $type = shift;
\&                bless {}, $type;
\&        }
\&        sub bar {
\&                my $self = shift;
\&                $self\->FOO::private::BAZ;
\&        }
\&
\&        package FOO::private;
\&
\&        sub BAZ {
\&                print "in BAZ\en";
\&        }
\&
\&        package main;
\&
\&        $a = FOO\->new;
\&        $a\->bar;
.Ve
.PP
Now we try to override the \s-1\fIBAZ\s0()\fR method.  We would like \fIFOO::bar()\fR to call
\&\s-1\fIGOOP::BAZ\s0()\fR, but this cannot happen because \fIFOO::bar()\fR explicitly calls
\&\fIFOO::private::BAZ()\fR.
.PP
.Vb 1
\&        package FOO;
\&
\&        sub new {
\&                my $type = shift;
\&                bless {}, $type;
\&        }
\&        sub bar {
\&                my $self = shift;
\&                $self\->FOO::private::BAZ;
\&        }
\&
\&        package FOO::private;
\&
\&        sub BAZ {
\&                print "in BAZ\en";
\&        }
\&
\&        package GOOP;
\&        @ISA = qw( FOO );
\&        sub new {
\&                my $type = shift;
\&                bless {}, $type;
\&        }
\&
\&        sub BAZ {
\&                print "in GOOP::BAZ\en";
\&        }
\&
\&        package main;
\&
\&        $a = GOOP\->new;
\&        $a\->bar;
.Ve
.PP
To create reusable code we must modify class \s-1FOO\s0, flattening class
FOO::private.  The next example shows a reusable class \s-1FOO\s0 which allows the
method \s-1\fIGOOP::BAZ\s0()\fR to be used in place of \s-1\fIFOO::BAZ\s0()\fR.
.PP
.Vb 1
\&        package FOO;
\&
\&        sub new {
\&                my $type = shift;
\&                bless {}, $type;
\&        }
\&        sub bar {
\&                my $self = shift;
\&                $self\->BAZ;
\&        }
\&
\&        sub BAZ {
\&                print "in BAZ\en";
\&        }
\&
\&        package GOOP;
\&        @ISA = qw( FOO );
\&
\&        sub new {
\&                my $type = shift;
\&                bless {}, $type;
\&        }
\&        sub BAZ {
\&                print "in GOOP::BAZ\en";
\&        }
\&
\&        package main;
\&
\&        $a = GOOP\->new;
\&        $a\->bar;
.Ve
.SH "CLASS CONTEXT AND THE OBJECT"
.IX Header "CLASS CONTEXT AND THE OBJECT"
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.
.PP
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.
.PP
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 (\*(L"Is it in my
class, or in a subclass?  Which subclass?\*(R"), and this can be inconvenient
and will lead to hackery.  It is better just to let the object tell the
method where that data is located.
.PP
.Vb 1
\&        package Bar;
\&
\&        %fizzle = ( \*(AqPassword\*(Aq => \*(AqXYZZY\*(Aq );
\&
\&        sub new {
\&                my $type = shift;
\&                my $self = {};
\&                $self\->{\*(Aqfizzle\*(Aq} = \e%fizzle;
\&                bless $self, $type;
\&        }
\&
\&        sub enter {
\&                my $self = shift;
\&
\&                # Don\*(Aqt 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\->{\*(Aqfizzle\*(Aq};
\&
\&                print "The word is ", $fizzle\->{\*(AqPassword\*(Aq}, "\en";
\&        }
\&
\&        package Foo;
\&        @ISA = qw( Bar );
\&
\&        %fizzle = ( \*(AqPassword\*(Aq => \*(AqRumple\*(Aq );
\&
\&        sub new {
\&                my $type = shift;
\&                my $self = Bar\->new;
\&                $self\->{\*(Aqfizzle\*(Aq} = \e%fizzle;
\&                bless $self, $type;
\&        }
\&
\&        package main;
\&
\&        $a = Bar\->new;
\&        $b = Foo\->new;
\&        $a\->enter;
\&        $b\->enter;
.Ve
.SH "INHERITING A CONSTRUCTOR"
.IX Header "INHERITING A CONSTRUCTOR"
An inheritable constructor should use the second form of \fIbless()\fR which allows
blessing directly into a specified class.  Notice in this example that the
object will be a \s-1BAR\s0 not a \s-1FOO\s0, even though the constructor is in class \s-1FOO\s0.
.PP
.Vb 1
\&        package FOO;
\&
\&        sub new {
\&                my $type = shift;
\&                my $self = {};
\&                bless $self, $type;
\&        }
\&
\&        sub baz {
\&                print "in FOO::baz()\en";
\&        }
\&
\&        package BAR;
\&        @ISA = qw(FOO);
\&
\&        sub baz {
\&                print "in BAR::baz()\en";
\&        }
\&
\&        package main;
\&
\&        $a = BAR\->new;
\&        $a\->baz;
.Ve
.SH "DELEGATION"
.IX Header "DELEGATION"
Some classes, such as SDBM_File, cannot be effectively subclassed because
they create foreign objects.  Such a class can be extended with some sort of
aggregation technique such as the \*(L"using\*(R" relationship mentioned earlier or
by delegation.
.PP
The following example demonstrates delegation using an \s-1\fIAUTOLOAD\s0()\fR function to
perform message-forwarding.  This will allow the Mydbm object to behave
exactly like an SDBM_File object.  The Mydbm class could now extend the
behavior by adding custom \s-1\fIFETCH\s0()\fR and \s-1\fISTORE\s0()\fR methods, if this is desired.
.PP
.Vb 1
\&        package Mydbm;
\&
\&        require SDBM_File;
\&        require Tie::Hash;
\&        @ISA = qw(Tie::Hash);
\&
\&        sub TIEHASH {
\&                my $type = shift;
\&                my $ref = SDBM_File\->new(@_);
\&                bless {\*(Aqdelegate\*(Aq => $ref};
\&        }
\&
\&        sub AUTOLOAD {
\&                my $self = shift;
\&
\&                # The Perl interpreter places the name of the
\&                # message in a variable called $AUTOLOAD.
\&
\&                # DESTROY messages should never be propagated.
\&                return if $AUTOLOAD =~ /::DESTROY$/;
\&
\&                # Remove the package name.
\&                $AUTOLOAD =~ s/^Mydbm:://;
\&
\&                # Pass the message to the delegate.
\&                $self\->{\*(Aqdelegate\*(Aq}\->$AUTOLOAD(@_);
\&        }
\&
\&        package main;
\&        use Fcntl qw( O_RDWR O_CREAT );
\&
\&        tie %foo, "Mydbm", "adbm", O_RDWR|O_CREAT, 0640;
\&        $foo{\*(Aqbar\*(Aq} = 123;
\&        print "foo\-bar = $foo{\*(Aqbar\*(Aq}\en";
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
perlboot, perltoot, perltooc.