sub someFunc {
  my @args = qw( client_number MM DD S );  # no commas here
  for (@args) {
    $_ = defined($_[0]) ? shift : die "$_ not defined";
  }
  # hooray
}
[download]

sub someFunc {
  my $args = [
    { client_number => 1, MM => 2, DD => 3, S => 4, },
  ];
  for (keys %$args) {
    my $idx = $args->[0]{$_} - 1;
    if (defined $_[$idx]) { $args->{$_} = $_[$idx], next }
    die "$_ not defined";
  }
  # hooray
}
[download]

If you don't mind changing the calling conventions of your subroutine, go a step further and use named arguments in the form of a hash:

sub someFunc {
   my %args = @_;
   my @arglist = qw{ client_number MM DD S };
   foreach (@arglist) {
      die "$_ not given" unless exists $args{$_};
   }

   # Now use $args{client_number} and $args{MM}
}
[download]

sub file_name {
  my %args;
  @args{qw/client_number MM DD S/} = @_;

  for (keys %args) {
    defined($args{$_}) or die "\$$_ not defined";
  }

  local $";
  "I@args{qw/client_number MM DD S/}";
}
[download]

I want to be able to ensure a set of variables will all have values before assigning them to @_

But that's not what you're doing here. You're checking that the values in @_ are defined before assigning them to your local variables using a horribly complex statement.

Do you have to know the variable name? Wouldn't the parameter number be enough to track down any problems? I'd probably wrtie it something like this:

use strict;

sub file_name {
  die "incorrect number of parameters\n"
    unless @_ == 4;

  for each (0 .. $#_) {
    die "invalid parameter [$_]\n"
      unless defined $_[$_];

  $" = '';

  "I@_"'
}
[download]

Oh, and the commas in your qw are probably a bug too.

"Perl makes the fun jobs fun
and the boring jobs bearable" - me

Wouldn't the parameter number be enough to track down any problems?

Well, if instead of passing in a list of constants, he might well be passing in enough arguments, but one of them have a value of undef (which, of course, the second bit of your code would catch).

Seems to me wanting the name of the invalid variable is one more step in princepawn's "the secretary should be able to use the program" ethic. Whether or not we agree with that aim is another matter =)

Philosophy can be made out of anything. Or less -- Jerry A. Fodor

Why not go the following route?

sub file_name {
    my ($client_number, $MM, $DD, $S) = @_;
    my @varnames = qw($client_number $MM $DD $S);
    for (my $i=0; $i <= scalar @_; $i++) {
        die "$varnames[$i] not defined\n" unless defined($_[$i]);
    }
    "I$client_number$MM$DD$S";
}
[download]

Philosophy can be made out of anything. Or less -- Jerry A. Fodor

The task itself does not seem to me to be particularly important. Personally I would take a hint from the fact that you felt a need for symbolic refs, apply the usual fix and put your variables in a hash.

*shrug*

use strict;

sub file_name {
  no strict 'vars';
  no strict 'refs';
  my @arg = qw(client_number MM DD S);
  for (@arg) {
    $$_ = defined($_[0]) ? shift : die "$_ not defined"
  }

  "I$client_number$MM$DD$S"
}

my $out = file_name 1,2,3,4;

warn $out;
[download]

But of course it can be improved with davorg's wonderful embellishment:

{ local $" "I@_" }
[download]

This code reminds me of learning shorthand.

Using davorg's little quoting nice-ness with a bit of finessing, we get:

sub someFunc {
  my $i;
  local $";
  for (qw( this that otherfield )) {
    die "$_ is undef" unless defined $_[$i++];
  }
  "@_";
}
[download]



japhy -- Perl and Regex Hacker

It'd be easier if you reply to my message, so I don't have to search for a response. ;)

Anyway, this code works for me:

#!/usr/bin/perl -w

use strict;

sub someFunc {
  my $args = [
    { client_number => 1, MM => 2, DD => 3, S => 4, },
  ];
  for (keys %$args) {
    my $idx = $args->[0]{$_} - 1;
    if (defined $_[$idx]) { $args->{$_} = $_[$idx], next }
    die "$_ not defined";
  }
  print "@$args\n";
}

someFunc(1,2,3,4);  # fine
someFunc(1,2,3);    # 'S' is not defined
[download]

It works under strict.

japhy -- Perl and Regex Hacker