Re: Passing hashes as arguments to a sub?

[jimbojones]

Hi
TheDamian's new book, Perl Best Practices, covers this in Chapter 9. He recommends passing a hash reference, typically to an anonymous hash.

my $foo = CalcFoo( { bar => 'abc', baz => 'def' } );

sub CalcFoo
{
  my $href = $_[0];

  my $foo;
  if ( defined $href->{bar} and defined $href->{baz} )
  {
    $foo = $href->{bar} . $href->{baz};
  }
  else
  {
    print "Error: pls define bar and baz\n";
  }
  return $foo;
}

The reasons given for not passing a list of raw key/value pairs is:

Requiring the named arguments to be specified inside a hash ensures that any mismatch, such as:

$line = padded({text=>$line, cols=>20..21, centered=>1, filler=>$SPACE
+});

will be reported (usually at compile time) in the caller’s context:

Odd number of elements in anonymous hash at demo.pl line 42

Passing those arguments as raw pairs:

$line = padded(text=>$line, cols=>20..21, centered=>1, filler=>$SPACE)
+;

would cause the exception to be thrown at run time, and from the line inside the subroutine where the odd number of arguments were unpacked and assigned to a hash:

The chapter on subroutines is currently available as a sample chapter on the O'Reilly website for you to peruse. It's a great book, highly recommended.

- j