perlboot.1

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 "PERLBOOT 1"
.TH PERLBOOT 1 "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.
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.SH "NAME"
perlboot \- Beginner's Object\-Oriented Tutorial
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
If you're not familiar with objects from other languages, some of the
other Perl object documentation may be a little daunting, such as
perlobj, a basic reference in using objects, and perltoot, which
introduces readers to the peculiarities of Perl's object system in a
tutorial way.
.PP
So, let's take a different approach, presuming no prior object
experience. It helps if you know about subroutines (perlsub),
references (perlref et. seq.), and packages (perlmod), so become
familiar with those first if you haven't already.
.Sh "If we could talk to the animals..."
.IX Subsection "If we could talk to the animals..."
Let's let the animals talk for a moment:
.PP
.Vb 9
\&    sub Cow::speak {
\&      print "a Cow goes moooo!\en";
\&    }
\&    sub Horse::speak {
\&      print "a Horse goes neigh!\en";
\&    }
\&    sub Sheep::speak {
\&      print "a Sheep goes baaaah!\en";
\&    }
\&
\&    Cow::speak;
\&    Horse::speak;
\&    Sheep::speak;
.Ve
.PP
This results in:
.PP
.Vb 3
\&    a Cow goes moooo!
\&    a Horse goes neigh!
\&    a Sheep goes baaaah!
.Ve
.PP
Nothing spectacular here.  Simple subroutines, albeit from separate
packages, and called using the full package name.  So let's create
an entire pasture:
.PP
.Vb 5
\&    # Cow::speak, Horse::speak, Sheep::speak as before
\&    @pasture = qw(Cow Cow Horse Sheep Sheep);
\&    foreach $animal (@pasture) {
\&      &{$animal."::speak"};
\&    }
.Ve
.PP
This results in:
.PP
.Vb 5
\&    a Cow goes moooo!
\&    a Cow goes moooo!
\&    a Horse goes neigh!
\&    a Sheep goes baaaah!
\&    a Sheep goes baaaah!
.Ve
.PP
Wow.  That symbolic coderef de-referencing there is pretty nasty.
We're counting on \f(CW\*(C`no strict subs\*(C'\fR mode, certainly not recommended
for larger programs.  And why was that necessary?  Because the name of
the package seems to be inseparable from the name of the subroutine we
want to invoke within that package.
.PP
Or is it?
.Sh "Introducing the method invocation arrow"
.IX Subsection "Introducing the method invocation arrow"
For now, let's say that \f(CW\*(C`Class\->method\*(C'\fR invokes subroutine
\&\f(CW\*(C`method\*(C'\fR in package \f(CW\*(C`Class\*(C'\fR.  (Here, \*(L"Class\*(R" is used in its
\&\*(L"category\*(R" meaning, not its \*(L"scholastic\*(R" meaning.) That's not
completely accurate, but we'll do this one step at a time.  Now let's
use it like so:
.PP
.Vb 4
\&    # Cow::speak, Horse::speak, Sheep::speak as before
\&    Cow\->speak;
\&    Horse\->speak;
\&    Sheep\->speak;
.Ve
.PP
And once again, this results in:
.PP
.Vb 3
\&    a Cow goes moooo!
\&    a Horse goes neigh!
\&    a Sheep goes baaaah!
.Ve
.PP
That's not fun yet.  Same number of characters, all constant, no
variables.  But yet, the parts are separable now.  Watch:
.PP
.Vb 2
\&    $a = "Cow";
\&    $a\->speak; # invokes Cow\->speak
.Ve
.PP
Ahh!  Now that the package name has been parted from the subroutine
name, we can use a variable package name.  And this time, we've got
something that works even when \f(CW\*(C`use strict refs\*(C'\fR is enabled.
.Sh "Invoking a barnyard"
.IX Subsection "Invoking a barnyard"
Let's take that new arrow invocation and put it back in the barnyard
example:
.PP
.Vb 9
\&    sub Cow::speak {
\&      print "a Cow goes moooo!\en";
\&    }
\&    sub Horse::speak {
\&      print "a Horse goes neigh!\en";
\&    }
\&    sub Sheep::speak {
\&      print "a Sheep goes baaaah!\en";
\&    }
\&
\&    @pasture = qw(Cow Cow Horse Sheep Sheep);
\&    foreach $animal (@pasture) {
\&      $animal\->speak;
\&    }
.Ve
.PP
There!  Now we have the animals all talking, and safely at that,
without the use of symbolic coderefs.
.PP
But look at all that common code.  Each of the \f(CW\*(C`speak\*(C'\fR routines has a
similar structure: a \f(CW\*(C`print\*(C'\fR operator and a string that contains
common text, except for two of the words.  It'd be nice if we could
factor out the commonality, in case we decide later to change it all
to \f(CW\*(C`says\*(C'\fR instead of \f(CW\*(C`goes\*(C'\fR.
.PP
And we actually have a way of doing that without much fuss, but we
have to hear a bit more about what the method invocation arrow is
actually doing for us.
.Sh "The extra parameter of method invocation"
.IX Subsection "The extra parameter of method invocation"
The invocation of:
.PP
.Vb 1
\&    Class\->method(@args)
.Ve
.PP
attempts to invoke subroutine \f(CW\*(C`Class::method\*(C'\fR as:
.PP
.Vb 1
\&    Class::method("Class", @args);
.Ve
.PP
(If the subroutine can't be found, \*(L"inheritance\*(R" kicks in, but we'll
get to that later.)  This means that we get the class name as the
first parameter (the only parameter, if no arguments are given).  So
we can rewrite the \f(CW\*(C`Sheep\*(C'\fR speaking subroutine as:
.PP
.Vb 4
\&    sub Sheep::speak {
\&      my $class = shift;
\&      print "a $class goes baaaah!\en";
\&    }
.Ve
.PP
And the other two animals come out similarly:
.PP
.Vb 8
\&    sub Cow::speak {
\&      my $class = shift;
\&      print "a $class goes moooo!\en";
\&    }
\&    sub Horse::speak {
\&      my $class = shift;
\&      print "a $class goes neigh!\en";
\&    }
.Ve
.PP
In each case, \f(CW$class\fR will get the value appropriate for that
subroutine.  But once again, we have a lot of similar structure.  Can
we factor that out even further?  Yes, by calling another method in
the same class.
.Sh "Calling a second method to simplify things"
.IX Subsection "Calling a second method to simplify things"
Let's call out from \f(CW\*(C`speak\*(C'\fR to a helper method called \f(CW\*(C`sound\*(C'\fR.
This method provides the constant text for the sound itself.
.PP
.Vb 7
\&    { package Cow;
\&      sub sound { "moooo" }
\&      sub speak {
\&        my $class = shift;
\&        print "a $class goes ", $class\->sound, "!\en";
\&      }
\&    }
.Ve
.PP
Now, when we call \f(CW\*(C`Cow\->speak\*(C'\fR, we get a \f(CW$class\fR of \f(CW\*(C`Cow\*(C'\fR in
\&\f(CW\*(C`speak\*(C'\fR.  This in turn selects the \f(CW\*(C`Cow\->sound\*(C'\fR method, which
returns \f(CW\*(C`moooo\*(C'\fR.  But how different would this be for the \f(CW\*(C`Horse\*(C'\fR?
.PP
.Vb 7
\&    { package Horse;
\&      sub sound { "neigh" }
\&      sub speak {
\&        my $class = shift;
\&        print "a $class goes ", $class\->sound, "!\en";
\&      }
\&    }
.Ve
.PP