[Koha-devel] Coding patterns discussion

[David Cook]

After reviewing  <http://search.cpan.org/~ether/Try-Tiny-0.27/lib/Try/Tiny.pm> http://search.cpan.org/~ether/Try-Tiny-0.27/lib/Try/Tiny.pm, I’d add a semi-colon to the end of that sample code, since catch {} apparently is just an argument to try():

 

“catch (&;@) Intended to be used in the second argument position of try.”

 

use Koha::Exceptions;
use Try::Tiny;
sub boom {
    Koha::Exceptions::Exception->throw;
}
try {
    boom();
} catch {
    if ( ref($_) eq 'Koha::Exceptions::Exception' ) {
        # Do that
    } elsif ( ref($_) eq 'Koha::Exceptions::AnotherException' ) {
        # do something else
    }
};

 

It’s the same gotcha that you get with eval {}; unfortunately. 

 

Interesting warning in the perldoc:

 

“The value of $_ in the catch block is not guaranteed to be the value of the exception thrown ($@) in the try block. There is no safe way to ensure this, since eval may be used unhygienically in destructors. The only guarantee is that the catch will be called if an exception is thrown.”

 

I suppose it should be safe enough though since we’re providing the exception classes ourselves…

 

David Cook

Systems Librarian

Prosentient Systems

72/330 Wattle St

Ultimo, NSW 2007

Australia

 

Office: 02 9212 0899

Direct: 02 8005 0595

 

From: koha-devel-bounces at lists.koha-community.org [mailto:koha-devel-bounces at lists.koha-community.org] On Behalf Of Tomas Cohen Arazi
Sent: Thursday, 15 September 2016 1:19 AM
To: Jonathan Druart <jonathan.druart at bugs.koha-community.org>; koha-devel <koha-devel at lists.koha-community.org>
Subject: Re: [Koha-devel] Coding patterns discussion

 

 

El mié., 14 sept. 2016 a las 4:58, Jonathan Druart (<jonathan.druart at bugs.koha-community.org <mailto:jonathan.druart at bugs.koha-community.org> >) escribió:

Hi,

We used to have problems with transactions, if they were used from the
a subroutine/method which was called from tests (which use
transactions as well), it did not work.
Two transactions could not be started together.

 

I recall nested transactions were problematic.

 

Now that we are using DBIx::Class transactions it works correctly and
we will be able to use it in the codebase everywhere we need it.
I try to use it as soon as it's useful (see
Koha::Acquisition::Currency->store and bug 16907
Koha::Patrons->delete).

 

Yes! The point of my email, was to highlight the possibility we now have, and gather opinions on how to better do it. I wanted to raise this on a dev meeting. We have a tradition of letting patches speak, but some healthy discussion about this could let us reach some consensus, and guide new devs into good coding practices.

 

Regarding the try-catch module, the following is fine by me:
use Koha::Exceptions;
use Try::Tiny;
sub boom {
    Koha::Exceptions::Exception->throw;
}
try {
    boom();
} catch {
    if ( ref($_) eq 'Koha::Exceptions::Exception' ) {
        # Do that
    } elsif ( ref($_) eq 'Koha::Exceptions::AnotherException' ) {
        # do something else
    }
}

 

Yes, I like the Try::Tiny lib and would propose to just start using it. Your code is simple to read, and a clear improvement! Koha::Virtualshelf already raises exceptions and shelves.pl <http://shelves.pl>  catches them on another way, in master!

I mentioned TryCatch only because its syntax is sexier IMHO, but the main point was, again, to highlight the possible use of some convenient try/catch lib on the Koha:: namespace, which in conjuntcion with transactions would make our code quite reliable and readable.

 

You should also have a look at Bug 13995 - Proper Exception handling

 

I will, I recall the bug got stuck because Olli introduced one file per exception. It is handy for editor's autocomplete features, but it looked awkward. That's why I propose splitting exceptions files on a per-package basis.

 

Cheers 

-- 

Tomás Cohen Arazi

Theke Solutions (https://theke.io <http://theke.io/> )
✆ +54 9351 3513384
GPG: B2F3C15F

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