>I want to read some information about AUTOLOAD in POD.
Hi,
Got these pieces from Schwartz's book and hope it helps.
After Perl searches the inheritance tree and UNIVERSAL for a method, it doesn't
just stop there if the search is unsuccessful. Perl repeats the search through
the very same hierarchy (including UNIVERSAL), looking for a method named
AUTOLOAD.
If an AUTOLOAD exists, the subroutine is called in place of the original
method, passing it the normal predetermined argument list: the class name or
instance reference, followed by any arguments provided to the method call. The
original method name is passed in the package variable called $AUTOLOAD (in the
package where the subroutine was compiled) and contains the fully qualified
method name, so you should generally strip everything up to the final double
colon if you want a simple method name.
The AUTOLOAD subroutine can execute the desired operation itself, install a
subroutine and then jump into it, or perhaps just die if asked to perform an
unknown method.
One use of AUTOLOAD defers the compilation of a large subroutine until it is
actually needed. For example, suppose the eat method for an animal is complex
but unused in nearly every invocation of the program. You can defer its
compilation as follows:
## in Animal
sub AUTOLOAD {
our $AUTOLOAD;
(my $method = $AUTOLOAD) =~ s/.*:://s; # remove package name
if ($method eq "eat") {
## define eat:
eval q{
sub eat {
...
long
definition
goes
here
...
}
}; # End of eval's q{ } string
die $@ if $@; # if typo snuck in
goto &eat; # jump into it
} else { # unknown method
croak "$_[0] does not know how to $method\n";
}
}
If the method name is eat, you'll define eat (which had previously been held in
a string but not compiled), and then jump into it with a special construct that
replaces the current subroutine invocation with an invocation to eat.[1] After
the first AUTOLOAD hit, the eat subroutine is now defined, so won't be coming
back here. This is great for compile-as-you-go programs because it minimizes
startup overhead.
[1] Although goto is generally (and rightfully) considered evil, this form of
goto, which gives a subroutine name as a target, is not really the evil goto;
it's the good goto.
For a more automated way of creating code to do this, which makes it easy to
turn the autoloading off during development and debugging, see the AutoLoader
and SelfLoader core module documentation.
--
Jeff Pang
NetEase AntiSpam Team
http://corp.netease.com
--
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
<http://learn.perl.org/> <http://learn.perl.org/first-response>
