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Comment by joeyh | Hacker News Reader

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 to audit code for this kind of thing is a real pain. I still maintain existing perl projects, but won't be starting any new ones.

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I think it's a pretty weak reason to give up on a language because you were using a global variable and expecting it to automatically be treated as a local variable within your function.

As others have mentioned, you are using a global variable ($_) inside a function. This is generally considered a bad practice.

The standard perl idiom of getting your function arguments via shift would make this a non-issue.

This is a feature, not a bug. And this is not _requirement_, it is up to you to use it. You are always free to pass parameters the way it would not happen..

This is not much different than mutating a global variable inside a function.

I would write your code as:

    foo($_) foreach @bar;

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

You can also fix this is to localize $_ inside the function, if you don't want to pass $_ as a parameter.

    foo foreach @bar;

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

You can even use $_ instead of $var (although it looks a little weird assigning $_ to itself):

    foo foreach @bar;

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

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.

Joey's example is bad (or, at best, fragile) Perl, but he's also written a fair amount of useful and popular code in Perl too.

Yes thanks.. to be clear, I have programmed in perl since 1995.

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