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Re^2: Perl::Critic says don't modify $_ in list functions and other things

by AnomalousMonk (Bishop)
on Jul 09, 2020 at 22:59 UTC ( #11119109=note: print w/replies, xml ) Need Help??


in reply to Re: Perl::Critic says don't modify $_ in list functions and other things
in thread Perl::Critic says don't modify $_ in list functions and other things

Does eval BLOCK act differently than eval EXPR?

Indeed it does. eval BLOCK is parsed at compile time; if there are any syntactic errors, compilation fails. eval EXPR is evaluated at run time; if there are any errors, the error message goes into $@ (see perlvar), the eval returns undef, and the Perl program is free to soldier on.


Give a man a fish:  <%-{-{-{-<

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Re^3: Perl::Critic says don't modify $_ in list functions and other things
by Lady_Aleena (Curate) on Jul 09, 2020 at 23:09 UTC

    I made a few changes to the conditionals around the eval code to possibly keep mistakes from happening when it is used, but I still can't figure out how to convert the eval EXPR into an eval BLOCK. Like converting a map or grep EXPR to a BLOCK, it isn't as easy as putting {} around it instead of () and expecting it to work the same.

    if ($raw_value && $raw_value =~ /\d+\*\d+/) { $total_value = eval($raw_value); # performs multiplication ($amount, $base_value) = split(/\*/,$raw_value); } elsif ($raw_value && $raw_value =~ /\d+\/\d+/) { $base_value = eval($raw_value); # performs division ($total_value, $amount) = split(/\//, $raw_value); } else { $amount = $raw_value; $base_value = $assets->{$lookup_asset} ? $assets->{$lookup_asset} +: 0; $total_value = $amount * $base_value; }

    My OS is Debian 10 (Buster); my perl versions are 5.28.1 local and 5.16.3 or 5.30.0 on web host depending on the shebang.

    No matter how hysterical I get, my problems are not time sensitive. So, relax, have a cookie, and a very nice day!
    Lady Aleena

      Are the numerical parts of $raw_value positive integers? If so, it's going to be simpler and (I suspect) more efficient to use capture groups and do the maths by hand. eg:

      #!/usr/bin/env perl use strict; use warnings; my $raw_value = shift @ARGV; my ($total_value, $base_value, $amount); my $assets = {}; my $lookup_asset = 'foo'; if ($raw_value && $raw_value =~ /(\d+)\*(\d+)/) { $total_value = $1 * $2; # performs multiplication ($amount, $base_value) = ($1, $2); } elsif ($raw_value && $raw_value =~ /(\d+)\/(\d+)/) { $base_value = $1 / $2; # performs division ($total_value, $amount) = ($1, $2); } else { $amount = $raw_value; $base_value = $assets->{$lookup_asset} ? $assets->{$lookup_asset} +: 0; $total_value = $amount * $base_value; } print "Amount: $amount\nBase: $base_value\nTotal: $total_value\nRaw: $ +raw_value\n";

      At least, that's how I would go about it.

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