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Re: Small examples of string eval

by ruzam (Curate)
on May 14, 2006 at 03:16 UTC ( #549287=note: print w/ replies, xml ) Need Help??

in reply to Small examples of string eval

I have two places where I use eval all the time. I think eval is the best choice in these situations, maybe someone has a better alternative (that doesn't require non-core modules).

1) retrieving stored hashes
I regularily used Data::Dumper to turn hashes into strings so they can be stored in a database for later retrieval. The string accurately represents the original hash with out my having to do a thing and it's safe to store anyway I have to, flat files, dbm, mysql. When the data is later retrieved, eval is the easiest way to get it back into a useful hash. Something like this:
use Data::Dumper; $Data::Dumper::Indent = 0; # no spaces tabs or other fluff $Data::Dumper::Purity = 1; # include code to recreate recursive refere +nces sub store_hash { my $hash_ref = shift; my $saved = Dumper($hash_ref); # store $saved somewhere } sub get_hash { # get $saved from somewhere my $VAR1; eval {$saved} return $VAR1 ? $VAR1 : {}; }

1) wrapping DBI calls to capture errors. Far as I know this is the recommended (only?) way to do this.
sub selectrow_array { my $dbh = shift; my $query = shift; my @result; eval { @result = $dbh->selectrow_array($query) }; return my_custom_error_handler("selectrow_array $query") if $@; return @result; }
More generically I guess you could say eval is the tool of choice when ever you have to call code beyond your control that may kill your script.
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Re^2: Small examples of string eval
by eyepopslikeamosquito (Chancellor) on May 14, 2006 at 03:43 UTC

    eval { @result = $dbh->selectrow_array($query) }; return my_custom_error_handler("selectrow_array $query") if $@;
    That is an example of block eval, not string eval; the OP was asking about string eval. There is wide agreement that block eval is a good thing in Perl 5 (for exception handling). Overloading eval with two different meanings in Perl 5 was unfortunate and is fixed in Perl 6, where block eval is spelled try.

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