Undefined array values

[Experienced but Undocumented]

Newbie question: I've got an array like so:
$foo{'bar'} = "test";

Is there a way to assign a default value to any undefined values? For
example, if the program requests $foo{'abc'} and we haven't defined it, for
the default value to be used?

Thanks

 

[Andreas Kahari]

Newbie question: I've got an array like so:
$foo{'bar'} = "test";

That's a hash, but never mind.

Is there a way to assign a default value to any undefined values? For
example, if the program requests $foo{'abc'} and we haven't defined it, for
the default value to be used?

You could do something like this:

$value = (exists $foo{'bar'} ? $foo{'bar'} : $defaultvalue);

where $defaultvalue is some default value. Look up the
documentation for the exist function ("perdoc -f exists") and
the ternary "?:" operator ("perldoc perlop").

 

[Steve Grazzini]

Newbie question: I've got an array like so:
$foo{'bar'} = "test";

That's usually called a hash (since the "array" is another of
Perl's basic data types, and it's not the one you mean).

Is there a way to assign a default value to any undefined values?
For example, if the program requests $foo{'abc'} and we haven't defined
it, for the default value to be used?

You could do it with TIEHASH --

{
package Hash:efault;
use Tie::Hash;
our @ISA = qw(Tie::ExtraHash);

sub TIEHANDLE {
my ($class, $default) = @_;
bless [{}, $default], $class;
}

sub FETCH {
my ($ref, $default) = @{ shift() };
my $key = shift;

exists $ref->{$key} ? $ref->{$key} : $default;
}
}

tie my %foo, 'Hash:efault', 42;
print $foo{bar};

 

[Steve Grazzini]

You could do it with TIEHASH [ ... ]

sub TIEHANDLE {

Silly of me; I guess that means you can just use the default
version of TIEHASH.

 

[Glenn Jackman]

Newbie question: I've got an array like so:
$foo{'bar'} = "test";

Is there a way to assign a default value to any undefined values? For
example, if the program requests $foo{'abc'} and we haven't defined it, for
the default value to be used?

$foo{$key} = $default unless exists $foo{$key};
or
$foo{$key} ||= $default;

The second is a different test: it assigns the default value if the
hash value is undefined. A hash key can exist but have an undefined
value:
$foo{bar} = "test";
$foo{abc} = undef;
@keys = keys %foo; # @keys is ('bar', 'abc') in some order

 

[Experienced but Undocumented]

That's a hash, but never mind.

What I meant *blushes*

 

[Experienced but Undocumented]

Newbie question: I've got an array like so:
$foo{'bar'} = "test";

Thanks for your prompt replies, everyone!

 

[Tad McClellan]

$foo{$key} = $default unless exists $foo{$key};
or
$foo{$key} ||= $default;

But neither of those do what the OP asked for.

He didn't say he wants to add entries to the hash.

He wants something other than undef to be returned when
exists() is false.

tie()ing is the way to go.