Get reference to newly-created array

benizi has asked for the wisdom of the Perl Monks concerning the following question:

I use Getopt::Long quite a bit, and I'm pretty fond of this idiom:

use Getopt::Long;
GetOptions(
    'thing=s' => \(my $thing = ''),
    'other=s' => \(my $other = ''),
    'flag'    => \(my $flag = 0),
) or die 'options'; # usually scripts are for my own use
[download]

The one thing that always bugged me about this approach is that I have to treat arrays differently. (I really like defining the scalars the way I've done it above. Makes it easy to add or delete them.) This fails:

use Getopt::Long;
GetOptions( 'array=s@' => \(my @array) ) or die 'options';
[download]

...because the backslash creates a list of references over its operands. Which, in the case of the newly created array, is the empty list. Is there a way to cleverly get the behavior I want? (a replacement for the "\(my @array)" part that would be equivalent in some sense to "my @array; \@array")

Comment on Get reference to newly-created array Select or Download Code

Replies are listed 'Best First'.
Re: Get reference to newly-created array by ikegami (Patriarch) on Oct 22, 2007 at 16:33 UTC
`[]` and `do { my @array; \@array }`, will both create an array and return a reference to it, but the array will be anonymous. No good. You could use prototype trickery to do what you want. `sub get_array_ref(\@) { $_[0] } GetOptions( 'array=s' => get_array_ref(my @array) ); print("@array\n");` [download] By the way, it's `=s` when you pass a reference to an array, and `=s@` when you pass a reference to a scalar. That opens up another possibility: `GetOptions( 'array=s@' => \(my $array) ); print("@$array\n");` [download]	[reply] [d/l] [select]
Re: Get reference to newly-created array by benizi (Hermit) on Oct 22, 2007 at 21:58 UTC
By the way, it's =s when you pass a reference to an array, and =s@ when you pass a reference to a scalar. Both seem to work and do what I want. Is there any particular reason to choose one over the other? $ cat test-gol.pl #!/usr/bin/perl use Getopt::Long qw/:config pass_through/; my ($array, @array); # option names are: [sa][nw] s=scalar, a=array n=no '@', w=with '@' GetOptions( 'sn=s' => \$array ) or die 'options'; print "Scalar @$array\n"; undef $array; GetOptions( 'sw=s@' => \$array ) or die 'options'; print "Scalar @$array\n"; GetOptions( 'an=s' => \@array ) or die 'options'; print "Array @array\n"; @array = (); GetOptions( 'aw=s@' => \@array ) or die 'options'; print "Array @array\n"; $ perl test-gol.pl --sn one --sn two --sw one --sw two --an one --an t +wo --aw one --aw two Scalar Scalar one two Array one two Array one two [download]	[reply] [d/l]
Re^2: Get reference to newly-created array by ikegami (Patriarch) on Oct 23, 2007 at 01:42 UTC
Both seem to work and do what I want. Is there any particular reason to choose one over the other? Yes. One is documented, and the other just happens to work at the moment.	[reply]
Re: Get reference to newly-created array by almut (Canon) on Oct 22, 2007 at 18:00 UTC
As long as you don't need to initialise the array, you should be fine if you simply omit the parentheses. For example `#!/usr/bin/perl use Getopt::Long; GetOptions( 'thing=s' => \(my $thing = ''), 'flag' => \(my $flag = 0), 'array=s' => \my @array, # no parens # ... ) or die 'options'; print "\@array: @array\n";` [download] when called as `$ ./646480.pl -a foo -a bar -a baz` [download] would print as expected `@array: foo bar baz` [download]	[reply] [d/l] [select]
Re: Get reference to newly-created array by benizi (Hermit) on Oct 22, 2007 at 23:32 UTC
Thanks, almut. That's exactly what I'm looking for.	[reply]


No such thing as a small change
	PerlMonks