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Ovid (2709)

Ovid
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Stuff with the Perl Foundation. A couple of patches in the Perl core. A few CPAN modules. That about sums it up.

Journal of Ovid (2709)

Tuesday January 28, 2003
05:59 PM

Grokking exceptions

[ #10249 ]

I didn't program Java for very long, so I really never quite understood the best way to handle exceptions. (The one thing that I miss in Perl is compile-time checking of whether or not the exceptions are caught, but that's a side issue). Recently, I was struggling to get an API just write (sic) and the simplest way to do it seemed to be the following:

my $data = $self->__validate_added_data;
if ( UNIVERSAL::isa( $data, 'Foo::Form' ) ) {
    # add the data
}
else {
    # process the error
}

In other words, if I get back a valid Form object, I can add the data to the database. Otherwise, I have a hashref that contains the form error information. This error information is user error -- not program error. As a result, I don't want to die or warn, yet variants of those are typical Perl error handling mechanisms. Further, I have a method that returns two fundamentally different types of data: and object or a hashref. I finally started using the Error.pm module and now use try/catch blocks to handle the types of errors that I need.

try {
    my $data = $self->__validate_added_data;
    # add the data
}
catch FormValidationError with {
    # process the error
};

Combining this with Test::Exception has made my tests simpler and my code more self-documenting. I'm going to have to dig up some resources on "Best Practices" with exception handling. I like this.

Hmm ... I think I'll post this on Perlmonks and see what they have to say.

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  • FWIW, I've noticed more discussion of whether checked exceptions in Java are worth the effort, particularly since they're not implemented in C#. There's a good writeup [mindview.net] on the issues from Bruce Eckel, along with some related discussion [mindview.net].
    • Absolutely wonderful writeup! That definitely makes the think that checked exceptions might not be the WunderTool that I thought. The problem appears to lie in programmers being pressed for time and thus "swallowing" exceptions with the intent to come back to them later. We all know what a lie "I'll do it tomorrow" is :)

      try {
        doSomethingWith(foo);
      } catch (SomeException e) {} /* exception swallowed */

      Knowing full well that I'm often under the gun at work, I could easily see myself doing t

  • Watch out for the closures issue with Error.pm. I wrote about this in my exceptions talk here [axkit.org].