Perl: When DWIM Doesn't

Post by prakashk » Tue, Jan 31, 2012, 6:39 PM UTC

joeyh wrote: post #17

I basically gave up on perl after discovering this: foo foreach @bar; sub foo { s/foo/bar/ print; } This clobbers the content of @bar due to mutating the $_ variable. Which is a useful feature. But imagine that foo, instead of directly mutating the value passed to it, calls into a complex set of other code. Now you have a bomb where working code can break in crazy ways if any of it gets changed to modify $_. Having t…

    foo($_) foreach @bar;

    sub foo {
        my $var = shift;
        $var =~ s/foo/bar/;
        print $var;
    }

    foo foreach @bar;

    sub foo {
        my $var = $_;
        $var =~ s/foo/bar/;
        print $var;
    }

    foo foreach @bar;

    sub foo {
        my $_ = $_;
        s/foo/bar/;
        print;
    }

Post by douglashunter » Tue, Jan 31, 2012, 7:26 PM UTC

mst wrote: post #20

pavelkaroukin wrote: post #19

Both OPs examples would be spotted by unit tests and finding actual bug after that is quite trivial. So I agree, you can trigger some features unpredictably, but this just shows power behind tool and remind you to be well self-organized =)

Frankly, the first one is a clear explanation of why you should have a config object not a hash. Don't use a freeform data structure for data that isn't actually freeform if you want the perl5 VM to be able to catch errors for you. Shutterstock are legendary round the perl community for being a hive of badly written ancient code that never gets significant refactoring effort though; combine this with a significant te…

Post by chromatic » Tue, Jan 31, 2012, 8:30 PM UTC

grout wrote: post #24

joeyh wrote: post #17

I basically gave up on perl after discovering this: foo foreach @bar; sub foo { s/foo/bar/ print; } This clobbers the content of @bar due to mutating the $_ variable. Which is a useful feature. But imagine that foo, instead of directly mutating the value passed to it, calls into a complex set of other code. Now you have a bomb where working code can break in crazy ways if any of it gets changed to modify $_. Having t…

You're funny. If this really pushed you over the edge, you were born -on- the edge, and didn't give Perl a fair shake.

Post by draegtun » Fri, Feb 03, 2012, 8:41 AM UTC

draegtun wrote: post #4

re: open() creating temporary file if file arg is undef Fortunately both IO::File (core module) & Path::Class don't do this: use IO::File; my $fh = IO::File->new( $config->{file_path}, 'r' ) or die "can't open $config->{file_path}: $!"; use Path::Class qw ; my $fh = file( $config->{file_path} )->openr; Both above spot the undef gotcha. NB. And ->openr() throws an exception. ref: https://metacpan.org/module/IO::File |…

    use strict;
    use warnings;
    use autodie;

    our $config;
    $config->{file_paht} = "somefile";

    open my $fh, '{file_path};