Re: how do modules work?

[drieux]

On Feb 17, 2004, at 5:07 PM, Andrew Gaffney wrote:

In my module, I created a function that connects to a MySQL database 
and then returns a DB handle. In the script that receives the DB 
handle, I removed the 'use DBI;' line. I can make queries against the 
database without problems. Why does this work?
I presume that you did the

        package My::DB
        use DBI;
and that your function is say

        sub do_get_db_handle
        {
                ....
                $dbh = DBI->connect($data_source, $user, $pass, $driver);
                ...
                $dbh;
        }
hence it is called like

        use My::DB;
        ...
        my $db = do_get_db_handle(@arglist);
        ...
        $rv  = $db->do($statement);
as Will has noted he thinks that the $dbh is a 'blessed' referece,
if you rummage around inside it you will find that yes, it is a
blessed reference. Since your module has already asserted the
	'use DBI'

it will have already both 'required' and 'imported' all of
the stuff 'needed' to understand what a blessed reference to
a DBI is all about.
As such your calling script did not need to make the 'use DBI'
since it would be required IN your module. This is a part of
how/why one likes to encapsulate things into perl modules so
that one can hide the common repeatively repeated redundent parts
without having to keep retyping them over and over and over again
in each new script that you need.
HTH.

ciao
drieux
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