attribute::handlers.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.

If the attribute name is unqualified, the attribute is installed in the
current package. Otherwise it is installed in the qualifier's package:
.PP
.Vb 1
\&        package Here;
\&
\&        use Attribute::Handlers autotie => {
\&                Other::Good => Tie::SecureHash, # tie attr installed in Other::
\&                        Bad => Tie::Taxes,      # tie attr installed in Here::
\&            UNIVERSAL::Ugly => Software::Patent # tie attr installed everywhere
\&        };
.Ve
.PP
Autoties are most commonly used in the module to which they actually tie, 
and need to export their attributes to any module that calls them. To
facilitate this, Attribute::Handlers recognizes a special \*(L"pseudo-class\*(R" \*(--
\&\f(CW\*(C`_\|_CALLER_\|_\*(C'\fR, which may be specified as the qualifier of an attribute:
.PP
.Vb 1
\&        package Tie::Me::Kangaroo:Down::Sport;
\&
\&        use Attribute::Handlers autotie => { \*(Aq_\|_CALLER_\|_::Roo\*(Aq => _\|_PACKAGE_\|_ };
.Ve
.PP
This causes Attribute::Handlers to define the \f(CW\*(C`Roo\*(C'\fR attribute in the package
that imports the Tie::Me::Kangaroo:Down::Sport module.
.PP
Note that it is important to quote the _\|_CALLER_\|_::Roo identifier because
a bug in perl 5.8 will refuse to parse it and cause an unknown error.
.PP
\fIPassing the tied object to \f(CI\*(C`tie\*(C'\fI\fR
.IX Subsection "Passing the tied object to tie"
.PP
Occasionally it is important to pass a reference to the object being tied
to the \s-1TIESCALAR\s0, \s-1TIEHASH\s0, etc. that ties it.
.PP
The \f(CW\*(C`autotie\*(C'\fR mechanism supports this too. The following code:
.PP
.Vb 2
\&        use Attribute::Handlers autotieref => { Selfish => Tie::Selfish };
\&        my $var : Selfish(@args);
.Ve
.PP
has the same effect as:
.PP
.Vb 1
\&        tie my $var, \*(AqTie::Selfish\*(Aq, @args;
.Ve
.PP
But when \f(CW"autotieref"\fR is used instead of \f(CW"autotie"\fR:
.PP
.Vb 2
\&        use Attribute::Handlers autotieref => { Selfish => Tie::Selfish };
\&        my $var : Selfish(@args);
.Ve
.PP
the effect is to pass the \f(CW\*(C`tie\*(C'\fR call an extra reference to the variable
being tied:
.PP
.Vb 1
\&        tie my $var, \*(AqTie::Selfish\*(Aq, \e$var, @args;
.Ve
.SH "EXAMPLES"
.IX Header "EXAMPLES"
If the class shown in \s-1SYNOPSIS\s0 were placed in the MyClass.pm
module, then the following code:
.PP
.Vb 2
\&        package main;
\&        use MyClass;
\&
\&        my MyClass $slr :Good :Bad(1**1\-1) :Omni(\-vorous);
\&
\&        package SomeOtherClass;
\&        use base MyClass;
\&
\&        sub tent { \*(Aqacle\*(Aq }
\&
\&        sub fn :Ugly(sister) :Omni(\*(Aqpo\*(Aq,tent()) {...}
\&        my @arr :Good :Omni(s/cie/nt/);
\&        my %hsh :Good(q/bye) :Omni(q/bus/);
.Ve
.PP
would cause the following handlers to be invoked:
.PP
.Vb 1
\&        # my MyClass $slr :Good :Bad(1**1\-1) :Omni(\-vorous);
\&
\&        MyClass::Good:ATTR(SCALAR)( \*(AqMyClass\*(Aq,          # class
\&                                    \*(AqLEXICAL\*(Aq,          # no typeglob
\&                                    \e$slr,              # referent
\&                                    \*(AqGood\*(Aq,             # attr name
\&                                    undef               # no attr data
\&                                    \*(AqCHECK\*(Aq,            # compiler phase
\&                                  );
\&
\&        MyClass::Bad:ATTR(SCALAR)( \*(AqMyClass\*(Aq,           # class
\&                                   \*(AqLEXICAL\*(Aq,           # no typeglob
\&                                   \e$slr,               # referent
\&                                   \*(AqBad\*(Aq,               # attr name
\&                                   0                    # eval\*(Aqd attr data
\&                                   \*(AqCHECK\*(Aq,             # compiler phase
\&                                 );
\&
\&        MyClass::Omni:ATTR(SCALAR)( \*(AqMyClass\*(Aq,          # class
\&                                    \*(AqLEXICAL\*(Aq,          # no typeglob
\&                                    \e$slr,              # referent
\&                                    \*(AqOmni\*(Aq,             # attr name
\&                                    \*(Aq\-vorous\*(Aq           # eval\*(Aqd attr data
\&                                    \*(AqCHECK\*(Aq,            # compiler phase
\&                                  );
\&
\&
\&        # sub fn :Ugly(sister) :Omni(\*(Aqpo\*(Aq,tent()) {...}
\&
\&        MyClass::UGLY:ATTR(CODE)( \*(AqSomeOtherClass\*(Aq,     # class
\&                                  \e*SomeOtherClass::fn, # typeglob
\&                                  \e&SomeOtherClass::fn, # referent
\&                                  \*(AqUgly\*(Aq,               # attr name
\&                                  \*(Aqsister\*(Aq              # eval\*(Aqd attr data
\&                                  \*(AqCHECK\*(Aq,              # compiler phase
\&                                );
\&
\&        MyClass::Omni:ATTR(CODE)( \*(AqSomeOtherClass\*(Aq,     # class
\&                                  \e*SomeOtherClass::fn, # typeglob
\&                                  \e&SomeOtherClass::fn, # referent
\&                                  \*(AqOmni\*(Aq,               # attr name
\&                                  [\*(Aqpo\*(Aq,\*(Aqacle\*(Aq]         # eval\*(Aqd attr data
\&                                  \*(AqCHECK\*(Aq,              # compiler phase
\&                                );
\&
\&
\&        # my @arr :Good :Omni(s/cie/nt/);
\&
\&        MyClass::Good:ATTR(ARRAY)( \*(AqSomeOtherClass\*(Aq,    # class
\&                                   \*(AqLEXICAL\*(Aq,           # no typeglob
\&                                   \e@arr,               # referent
\&                                   \*(AqGood\*(Aq,              # attr name
\&                                   undef                # no attr data
\&                                   \*(AqCHECK\*(Aq,             # compiler phase
\&                                 );
\&
\&        MyClass::Omni:ATTR(ARRAY)( \*(AqSomeOtherClass\*(Aq,    # class
\&                                   \*(AqLEXICAL\*(Aq,           # no typeglob
\&                                   \e@arr,               # referent
\&                                   \*(AqOmni\*(Aq,              # attr name
\&                                   ""                   # eval\*(Aqd attr data 
\&                                   \*(AqCHECK\*(Aq,             # compiler phase
\&                                 );
\&
\&
\&        # my %hsh :Good(q/bye) :Omni(q/bus/);
\&                                  
\&        MyClass::Good:ATTR(HASH)( \*(AqSomeOtherClass\*(Aq,     # class
\&                                  \*(AqLEXICAL\*(Aq,            # no typeglob
\&                                  \e%hsh,                # referent
\&                                  \*(AqGood\*(Aq,               # attr name
\&                                  \*(Aqq/bye\*(Aq               # raw attr data
\&                                  \*(AqCHECK\*(Aq,              # compiler phase
\&                                );
\&                        
\&        MyClass::Omni:ATTR(HASH)( \*(AqSomeOtherClass\*(Aq,     # class
\&                                  \*(AqLEXICAL\*(Aq,            # no typeglob
\&                                  \e%hsh,                # referent
\&                                  \*(AqOmni\*(Aq,               # attr name
\&                                  \*(Aqbus\*(Aq                 # eval\*(Aqd attr data
\&                                  \*(AqCHECK\*(Aq,              # compiler phase
\&                                );
.Ve
.PP
Installing handlers into \s-1UNIVERSAL\s0, makes them...err..universal.
For example:
.PP
.Vb 2
\&        package Descriptions;
\&        use Attribute::Handlers;
\&
\&        my %name;
\&        sub name { return $name{$_[2]}||*{$_[1]}{NAME} }
\&
\&        sub UNIVERSAL::Name :ATTR {
\&                $name{$_[2]} = $_[4];
\&        }
\&
\&        sub UNIVERSAL::Purpose :ATTR {
\&                print STDERR "Purpose of ", &name, " is $_[4]\en";
\&        }
\&
\&        sub UNIVERSAL::Unit :ATTR {
\&                print STDERR &name, " measured in $_[4]\en";
\&        }
.Ve
.PP
Let's you write:
.PP
.Vb 1
\&        use Descriptions;
\&
\&        my $capacity : Name(capacity)
\&                     : Purpose(to store max storage capacity for files)
\&                     : Unit(Gb);
\&
\&
\&        package Other;
\&
\&        sub foo : Purpose(to foo all data before barring it) { }
\&
\&        # etc.
.Ve
.SH "DIAGNOSTICS"
.IX Header "DIAGNOSTICS"
.ie n .IP """Bad attribute type: ATTR(%s)""" 4
.el .IP "\f(CWBad attribute type: ATTR(%s)\fR" 4
.IX Item "Bad attribute type: ATTR(%s)"
An attribute handler was specified with an \f(CW\*(C`:ATTR(\f(CIref_type\f(CW)\*(C'\fR, but the
type of referent it was defined to handle wasn't one of the five permitted:
\&\f(CW\*(C`SCALAR\*(C'\fR, \f(CW\*(C`ARRAY\*(C'\fR, \f(CW\*(C`HASH\*(C'\fR, \f(CW\*(C`CODE\*(C'\fR, or \f(CW\*(C`ANY\*(C'\fR.
.ie n .IP """Attribute handler %s doesn\*(Aqt handle %s attributes""" 4
.el .IP "\f(CWAttribute handler %s doesn\*(Aqt handle %s attributes\fR" 4
.IX Item "Attribute handler %s doesnt handle %s attributes"
A handler for attributes of the specified name \fIwas\fR defined, but not
for the specified type of declaration. Typically encountered whe trying
to apply a \f(CW\*(C`VAR\*(C'\fR attribute handler to a subroutine, or a \f(CW\*(C`SCALAR\*(C'\fR
attribute handler to some other type of variable.
.ie n .IP """Declaration of %s attribute in package %s may clash with future reserved word""" 4
.el .IP "\f(CWDeclaration of %s attribute in package %s may clash with future reserved word\fR" 4
.IX Item "Declaration of %s attribute in package %s may clash with future reserved word"
A handler for an attributes with an all-lowercase name was declared. An
attribute with an all-lowercase name might have a meaning to Perl
itself some day, even though most don't yet. Use a mixed-case attribute
name, instead.
.ie n .IP """Can\*(Aqt have two ATTR specifiers on one subroutine""" 4
.el .IP "\f(CWCan\*(Aqt have two ATTR specifiers on one subroutine\fR" 4
.IX Item "Cant have two ATTR specifiers on one subroutine"
You just can't, okay?
Instead, put all the specifications together with commas between them
in a single \f(CW\*(C`ATTR(\f(CIspecification\f(CW)\*(C'\fR.
.ie n .IP """Can\*(Aqt autotie a %s""" 4
.el .IP "\f(CWCan\*(Aqt autotie a %s\fR" 4
.IX Item "Cant autotie a %s"
You can only declare autoties for types \f(CW"SCALAR"\fR, \f(CW"ARRAY"\fR, and
\&\f(CW"HASH"\fR. They're the only things (apart from typeglobs \*(-- which are
not declarable) that Perl can tie.
.ie n .IP """Internal error: %s symbol went missing""" 4
.el .IP "\f(CWInternal error: %s symbol went missing\fR" 4
.IX Item "Internal error: %s symbol went missing"
Something is rotten in the state of the program. An attributed
subroutine ceased to exist between the point it was declared and the point
at which its attribute handler(s) would have been called.
.ie n .IP """Won\*(Aqt be able to apply END handler""" 4
.el .IP "\f(CWWon\*(Aqt be able to apply END handler\fR" 4
.IX Item "Wont be able to apply END handler"
You have defined an \s-1END\s0 handler for an attribute that is being applied
to a lexical variable.  Since the variable may not be available during \s-1END\s0
this won't happen.
.SH "AUTHOR"
.IX Header "AUTHOR"
Damian Conway ([e-mail])
.SH "BUGS"
.IX Header "BUGS"
There are undoubtedly serious bugs lurking somewhere in code this funky :\-)
Bug reports and other feedback are most welcome.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
.Vb 3
\&         Copyright (c) 2001, Damian Conway. All Rights Reserved.
\&       This module is free software. It may be used, redistributed
\&           and/or modified under the same terms as Perl itself.
.Ve