next.3

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.

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.\" ========================================================================
.\"
.IX Title "NEXT 3"
.TH NEXT 3 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
NEXT.pm \- Provide a pseudo\-class NEXT (et al) that allows method redispatch
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&    use NEXT;
\&
\&    package A;
\&    sub A::method   { print "$_[0]: A method\en";   $_[0]\->NEXT::method() }
\&    sub A::DESTROY  { print "$_[0]: A dtor\en";     $_[0]\->NEXT::DESTROY() }
\&
\&    package B;
\&    use base qw( A );
\&    sub B::AUTOLOAD { print "$_[0]: B AUTOLOAD\en"; $_[0]\->NEXT::AUTOLOAD() }
\&    sub B::DESTROY  { print "$_[0]: B dtor\en";     $_[0]\->NEXT::DESTROY() }
\&
\&    package C;
\&    sub C::method   { print "$_[0]: C method\en";   $_[0]\->NEXT::method() }
\&    sub C::AUTOLOAD { print "$_[0]: C AUTOLOAD\en"; $_[0]\->NEXT::AUTOLOAD() }
\&    sub C::DESTROY  { print "$_[0]: C dtor\en";     $_[0]\->NEXT::DESTROY() }
\&
\&    package D;
\&    use base qw( B C );
\&    sub D::method   { print "$_[0]: D method\en";   $_[0]\->NEXT::method() }
\&    sub D::AUTOLOAD { print "$_[0]: D AUTOLOAD\en"; $_[0]\->NEXT::AUTOLOAD() }
\&    sub D::DESTROY  { print "$_[0]: D dtor\en";     $_[0]\->NEXT::DESTROY() }
\&
\&    package main;
\&
\&    my $obj = bless {}, "D";
\&
\&    $obj\->method();             # Calls D::method, A::method, C::method
\&    $obj\->missing_method(); # Calls D::AUTOLOAD, B::AUTOLOAD, C::AUTOLOAD
\&
\&    # Clean\-up calls D::DESTROY, B::DESTROY, A::DESTROY, C::DESTROY
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\s-1NEXT\s0.pm adds a pseudoclass named \f(CW\*(C`NEXT\*(C'\fR to any program
that uses it. If a method \f(CW\*(C`m\*(C'\fR calls \f(CW\*(C`$self\->NEXT::m()\*(C'\fR, the call to
\&\f(CW\*(C`m\*(C'\fR is redispatched as if the calling method had not originally been found.
.PP
In other words, a call to \f(CW\*(C`$self\->NEXT::m()\*(C'\fR resumes the depth-first,
left-to-right search of \f(CW$self\fR's class hierarchy that resulted in the
original call to \f(CW\*(C`m\*(C'\fR.
.PP
Note that this is not the same thing as \f(CW\*(C`$self\->SUPER::m()\*(C'\fR, which
begins a new dispatch that is restricted to searching the ancestors
of the current class. \f(CW\*(C`$self\->NEXT::m()\*(C'\fR can backtrack
past the current class \*(-- to look for a suitable method in other
ancestors of \f(CW$self\fR \*(-- whereas \f(CW\*(C`$self\->SUPER::m()\*(C'\fR cannot.
.PP
A typical use would be in the destructors of a class hierarchy,
as illustrated in the synopsis above. Each class in the hierarchy
has a \s-1DESTROY\s0 method that performs some class-specific action
and then redispatches the call up the hierarchy. As a result,
when an object of class D is destroyed, the destructors of \fIall\fR
its parent classes are called (in depth-first, left-to-right order).
.PP
Another typical use of redispatch would be in \f(CW\*(C`AUTOLOAD\*(C'\fR'ed methods.
If such a method determined that it was not able to handle a
particular call, it might choose to redispatch that call, in the
hope that some other \f(CW\*(C`AUTOLOAD\*(C'\fR (above it, or to its left) might
do better.
.PP
By default, if a redispatch attempt fails to find another method
elsewhere in the objects class hierarchy, it quietly gives up and does
nothing (but see \*(L"Enforcing redispatch\*(R"). This gracious acquiescence
is also unlike the (generally annoying) behaviour of \f(CW\*(C`SUPER\*(C'\fR, which
throws an exception if it cannot redispatch.
.PP
Note that it is a fatal error for any method (including \f(CW\*(C`AUTOLOAD\*(C'\fR)
to attempt to redispatch any method that does not have the
same name. For example:
.PP
.Vb 1
\&        sub D::oops { print "oops!\en"; $_[0]\->NEXT::other_method() }
.Ve
.Sh "Enforcing redispatch"
.IX Subsection "Enforcing redispatch"
It is possible to make \f(CW\*(C`NEXT\*(C'\fR redispatch more demandingly (i.e. like
\&\f(CW\*(C`SUPER\*(C'\fR does), so that the redispatch throws an exception if it cannot
find a \*(L"next\*(R" method to call.
.PP
To do this, simple invoke the redispatch as:
.PP
.Vb 1
\&        $self\->NEXT::ACTUAL::method();
.Ve
.PP
rather than:
.PP
.Vb 1
\&        $self\->NEXT::method();
.Ve
.PP
The \f(CW\*(C`ACTUAL\*(C'\fR tells \f(CW\*(C`NEXT\*(C'\fR that there must actually be a next method to call,
or it should throw an exception.
.PP
\&\f(CW\*(C`NEXT::ACTUAL\*(C'\fR is most commonly used in \f(CW\*(C`AUTOLOAD\*(C'\fR methods, as a means to
decline an \f(CW\*(C`AUTOLOAD\*(C'\fR request, but preserve the normal exception-on-failure 
semantics:
.PP
.Vb 8
\&        sub AUTOLOAD {
\&                if ($AUTOLOAD =~ /foo|bar/) {
\&                        # handle here
\&                }
\&                else {  # try elsewhere
\&                        shift()\->NEXT::ACTUAL::AUTOLOAD(@_);
\&                }
\&        }
.Ve
.PP
By using \f(CW\*(C`NEXT::ACTUAL\*(C'\fR, if there is no other \f(CW\*(C`AUTOLOAD\*(C'\fR to handle the
method call, an exception will be thrown (as usually happens in the absence of
a suitable \f(CW\*(C`AUTOLOAD\*(C'\fR).
.Sh "Avoiding repetitions"
.IX Subsection "Avoiding repetitions"
If \f(CW\*(C`NEXT\*(C'\fR redispatching is used in the methods of a \*(L"diamond\*(R" class hierarchy:
.PP
.Vb 5
\&        #     A   B
\&        #    / \e /
\&        #   C   D