Try::Tiny vs. TryCatch: assigning a value to a variable inside of the try-block

v_melnik has asked for the wisdom of the Perl Monks concerning the following question:

I almost have no hope that there is a way to achieve what I want, but I'd better ask more experienced colleagues than make a mistake.

I like Try::Tiny very much, because it makes possible to do so something like that:

my $result = try {
  SomeClass->new
} catch {
  warn
};
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Alas, we can't do it with TryCatch, because it doesn't return the result the try-block, so TryCatch forces us to do something like that:

my $result;
try {
  $result = SomeClass->new
} catch {
  warn
};
[download]

As for me, TryCatch is better, because it allows us to control the flow by return/next/last and other commands and it can choose the catch-block depending on the class of the exception (I really love this feature!), but the only thing I can't bear with - that I must declare the resulting variable by a separate my-command before to use try.

What do you think, is there any ways to make the try-block to return a value?

Thank you!

UPD:Lots of thanks for all ideas. I decided to keep using TryCatch, but I'll declare all variables in the beginning of the block:

sub some_sub {
  my $foo;
  my $bar;
  my $baz;
# ...
  try {
    $foo = SomeClass->new;
  }
# ...
  try {
    $bar = $foo->old;
  }
# ...
  try {
    $baz = $bar->rotten;
  }
# ...
}
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I think, declaring all variables in the beginning of a block is a pretty good manner. Some of languages are quite strict about that, so I can just stop indulging myself with declaring them wherever I want. :)

V.Melnik

Comment on Try::Tiny vs. TryCatch: assigning a value to a variable inside of the try-block Select or Download Code

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Re: Try::Tiny vs. TryCatch: assigning a value to a variable inside of the try-block
by Athanasius (Archbishop) on Oct 08, 2014 at 15:07 UTC

Hello v_melnik,

Have you looked at Try::Tiny::ByClass? From the documentation:

... it provides a way to catch only some exceptions by filtering on the class (including superclasses and consumed roles) of an exception object.

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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Re: Try::Tiny vs. TryCatch: assigning a value to a variable inside of the try-block
by tobyink (Canon) on Oct 08, 2014 at 21:18 UTC

I don't think this satisfies all your criteria, but I've just spotted another one on the CPAN which looks promising... Syntax::Feature::Try.

toby döt ink

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Re: Try::Tiny vs. TryCatch: assigning a value to a variable inside of the try-block
by thanos1983 (Parson) on Oct 08, 2014 at 15:19 UTC

Hello v_melnink,

Update: I did not see Athanasius reply. Possibly is something that you are looking for.

I am not really sure what you are trying to achieve but a few points that I have noticed.

Alas, we can't do it with TryCatch,

Are you referring to Try::Tiny or to Error::TryCatch?

I can not understand what you are trying to achieve so I created a small sample of code that probably it will not help you but probably can help you describe what you are truing to do.

#!/usr/bin/perl
use strict;
use warnings;
use Try::Tiny;

sub normal {

    open my $normal , ">" , "normal.txt" or die $!;

    print $normal "This is just a sample\n";

    close $normal or die $!;

}

normal();

sub handle {

    open my $handle , ">" , "handle.txt";
    my $open = try {
        die $!;
    } catch {
    warn "caught error: $_"; # not $@
    };

    print "\$open: ".$open."\n";

    print $handle "This is another sample\n";

    close $handle;
    my $close = try {
        die $!;
    } catch {
    warn "caught error: $_"; # not $@
    };

    print "\$close: ".$close."\n";
}

handle();

__END__

caught error: Inappropriate ioctl for device at try::tint.pl line 22.
$open: 1
caught error: Inappropriate ioctl for device at try::tint.pl line 33.
$close: 1
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Take a look also on alternative modules, Error::TryCatch and Error. Maybe you fill find some functionality that you where looking for.

Seeking for Perl wisdom...on the process of learning...not there...yet!

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Re^2: Try::Tiny vs. TryCatch: assigning a value to a variable inside of the try-block

by tobyink (Canon) on Oct 08, 2014 at 18:31 UTC

"Are you referring to Try::Tiny or to Error::TryCatch?"

No... TryCatch.

It's pretty awesome, but a little slow, and very heavy on the dependencies.

toby döt ink

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Re: Try::Tiny vs. TryCatch: assigning a value to a variable inside of the try-block
by boftx (Deacon) on Oct 09, 2014 at 05:56 UTC

With regard to choosing the catch block based on the class of the exception thrown (I presume you are using something like Class::Exception or Throwable) have you considered a dispatch table?

# this is a very crude concept example

my $val = try {
    some_operation();
}
catch {
    if ( blessed($_) ) {
        &{$exceptions_by_class{blessed($_)}}($_);
    }
    else {
        # handle normal die or croak message
        ...
    }
};
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I must confess that I am a big fan of Try::Tiny and have not played with TryCatch.

Update: fixed typo in code.

You must always remember that the primary goal is to drain the swamp even when you are hip-deep in alligators.

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[d/l]


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