Question

When I run a simple bit of code like this:

my @arr=(1..5);
my $x;
foreach $x (@arr) {
    $x+=10;
}
print "@arr";

The result is “11 12 13 14 15” because $x “becomes” each element in the @arr array in the foreach. Well enough.

But here’s my thing… not so much a problem (the solution is easy, but inelegant, and I want my perl to be as elegant as possible).

I wrote a tie module for dealing with COBOL data. It takes a copybook, parses the fields, and then attaches that to a scalar/string so that access to/from the tied hash will return/set values in the string. It works wonderfully.

my %h,$rec;
my $cb=<<END;
       01 CH-RECORD.
          05 JOB-NUM PIC X.
          05 FILLER  PIC X(76).
          05 REC-TYPE PIC X(2).
END
tie %h, 'COBOLDataTie',$cb,\$rec; #tie the hash to the record via the copybook

From there, I can move a COBOL record to $rec and access the COBOL fields with the %h hash.

Again, this works perfectly. But the problem comes when I want to iterate over, say, an array of COBOL records. So if after the above code I had something akin to:

foreach $rec (@arr) {
    print "Job is ",$h{'JOB-NUM'},"\n";
}

it won’t work because the foreach actually changes the location of $rec, which breaks the tie on it. I end up having to do something like this:

foreach (@arr) {
    $rec=$_;
    print "Job is ",$h{'JOB-NUM'},"\n";
}

Is there any way I can do the “foreach $rec (@arr)” and not break my tied hash?

(And before anyone says, yes I know this begs for a nice object-oriented solution… some day I’ll get to that; I just have to find some time first)

EPILOGUE: I revised the TieHash code to, instead of pointing to an external record, it intercepts “special” keys for the hash, among which is ‘record’. So when I assign a record string to $h{‘record’} it’s the same as loading $rec in the example above. This is a far better solution, more self-contained. It also exposes a more OOP-like interface.

Answer 1

It seems like the best way is to do something like:

for (my $i=0;($rec=$arr[$i], $i<@arr);$i++) {

Not exactly the elegance I was hoping for, but it seems to work.