On 3 July 2015 at 19:18, ayush kabra <ayush.kab...@gmail.com> wrote:
> I want to make customized module on perl but i don't know how to make it. i
> have checked on google but it's little bit confusing. i am not able to
> understand what is the meaning of EXPORTER_OK ,IMPORT and there is lot of
> thinh which i am not able to understand. Can you please send me some
> examples of cusotmized module and explain it's functionality. what is the
> work of @ISA, and @INA path?.
If you look in the manual for `perldoc -f use`, you'll see that "use"
is a shorthand implies that a function called "import" will get called
if such a one exists.
Exporter.pm ( perldoc Exporter ) is a module that provides a stock
version of this function, with some standard customizable settings:
@EXPORT_OK is a "global" package variable with no /inherent/ meaning.
However, if you're calling the "import" function provided by Exporter,
that function will poke around in your package, and look for that
variable, and use that variable to decide which functions to export.
The question is, how does your package get this magic by exporter?
Where How does Expoter.pm's import get called?
That's where @ISA comes in, but doesn't have to.
@ISA is a special variable used by Perl to dictate the inheritance of
perl packages.
So:
package Foo;
sub foo { print "This is Foo::foo" }
package Bar;
sub bar { print "This if Bar::bar" }
package Quux;
@ISA = ('Foo');
sub quux { print "This is Quux::quux"; }
Here,
Quux ->quux # prints
Bar->bar # prints
Foo->foo # prints
Bar->foo # does not work, there's no 'foo'
Quux->foo # DOES work, because finding no 'foo' in Quux, it looks
up @ISA and finds 'foo' in Foo and calls that instead.
So:
Putting it all together:
package Example;
require Exporter;
our @ISA = ('Exporter');
our @EXPORT_OK = ("example_sub");
sub example_sub { print "hello" };
In some script:
package myscript;
use Example ('example_sub');
example_sub();
How this flows:
use Example ('example_sub'); -> triggers at BEGIN phase
# Example.pm is required
# Example->import() is checked for
# Example->import is found in Exporter.pm by looking up @ISA
# Exporter::import('Example', 'example_sub' ) gets called
# Exporter finds @Example::EXPORT_OK
# Exporter sees 'example_sub' in @EXPORT_OK
# Exporter sees you passed 'example_sub' to import
# Exporter creates 'myscript::example_sub' as a reference to
Example::example_sub
# Exporter returns from import
example_sub(); # Calls the imported Example::example_sub and
prints "hello"
This is all covered in much more depth in
perldoc perlmod
perldoc -f use
perldoc Exporter
--
Kent
KENTNL - https://metacpan.org/author/KENTNL
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