Dear monks,

Here is a code snippet that basically rollsup a line until the keyword end; is reached then it prints it out. I believe the approach i am taking is called a closure (please correct me if i am wrong). 

#!/usr/bin/perl

use strict;
use warnings;

my $dummy = "";
my $rollup = combine("");
my $oneline;

while (<DATA>) {
    $rollup->($_);

    # once end is reached store it in a variable    
    # reset variable-in-sub for next iteration
    if (/end;/) {
        # breaks if I remove $dummy and replace it with ""
        $oneline = $rollup->($dummy);
        $rollup = combine("");
        print $oneline,$/;
    }
}


sub combine {
    my $concat = shift;
    return sub {
        chomp($_[0]);
        $concat .= $_[0];
        return ($concat);
    }
}

[download]
__DATA__
line1;
line2;
line3;
end;
line4;
line5;
end;

[download]
Expected Output: 

line1;line2;line3;end;
line4;line5;end;

[download]

The above code works just fine but when I use $oneline = $rollup->(""); instead of $oneline = $rollup->($dummy);

I get the following error - 

Modification of a read-only value attempted at closure line 26, <DATA>
+ line 4.

[download]

Could you please explain to me what is the read-only value here?

I know i could do this whole step in a while loop and concatenate until end; is reached but wanted the flexibility in a sub and this also helps me learn more about closures :)

Thanks very much!

SK

Update: I have changed the title and took out the word closure as the problem is nothing to do with that.

In reply to Modification of read-only value error by sk

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