On Mon, Apr 09, 2012 at 12:59:04PM +0300, Shlomi Fish wrote:
> Hi xiaolan,
>
> On Mon, 9 Apr 2012 16:13:36 +0800
> xiaolan <practicalp...@gmail.com> wrote:
>
> > Hi,
> >
> > I just want to send email using MIME::Lite with Net::SMTP::SSL.
> > But MIME::Lite is going only with Net::SMTP by default.
> > So I searched and found a hack:
> >
> > use Net::SMTP::SSL;
> > BEGIN { @MIME::Lite::SMTP::ISA = qw(Net::SMTP::SSL); }
> >
> > This does work, now I can send messages with SMTPs.
> > But how does this work? Thank you.
> >
>
> The @ISA variable (which is specific for each package) determines which
> packages
> the current package inherits from. Note that in Perl 5, classes are
> implemented as packages. One can mutate the inheritance graph at run-time by
> changing the @ISA's of the various packages involved. This is usually not
> recommended, but as you demonstrate here - it is still useful.
>
> There's more information about it in the various perldocs, and some older
> tutorials (and the book Modern Perl covers it too), but there are more
> recommended ways to initially populate the packages’ @ISA, namely the
> extends()
> function when using Moose or friends, and "use base" (and the more modern "use
> parent") when not.
>
The parent examples on perldoc.perl.org[1] show this
package Baz;
use parent qw(Foo Bar);
is 'mostly similar' to
package Baz;
BEGIN {
require Foo;
require Bar;
push @ISA, qw(Foo Bar);
}
which nicely answers my worry about the override being overridden.
It seems that parent causes Baz to inherit Foo and Bar ; it doesn't override
anything inherited by Foo or Bar and I don't see anything in the base[2] and
parent documentation to show eiher can do this.
xiaolan's orginal code overwrites the parent classes of MIME::Lite::SMTP to
access the SSL socket layer. It's not inheriting but altering the inheritance
of a class/module being used.
To be safe xiaolan's BEGIN code should have
BEGIN{
## make sure required modules are loaded
require MIME::Lite;
require Net::SMTP::SSL;
## override the default socket layer in MIME::Lite
@MIME::Lite::SMTP::ISA = qw(Net::SMTP::SSL);
}
Kind regards
Lesley
[1]http://perldoc.perl.org/parent.html
[2]http://perldoc.perl.org/base.html
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