在标量语境中展平Perl数组的方法

Question

I recently started learning perl and have a question that I'm not finding a clear answer to on the Internet. say I have something like this,

@arr = (1, 2, 3);
$scal = "@arr"
# $scal is now 123.

Is the use of quotes the only way to flatten the array so that each element is stored in the scalar value? It seems improbable but I haven't found any other ways of doing this. Thanks in advance.

Answer 1

The join function is commonly used to "flatten" lists. Lets you specify what you want between each element in the resulting string.

$scal = join(",", @arr);
# $scal is no "1,2,3"

Answer 2

In your example, you're interpolating an array in a double-quoted string. What happens in those circumstances is is controlled by Perl's $" variable. From perldoc perlvar :

$LIST_SEPARATOR

$"

When an array or an array slice is interpolated into a double-quoted string or a similar context such as /.../ , its elements are separated by this value. Default is a space. For example, this:

print "The array is: @array\\n";

is equivalent to this:

print "The array is: " . join($", @array) . "\\n";

Mnemonic: works in double-quoted context.

The default value for $" is a space. You can obviously change the value of $" .

{
  local $" = ':',
  my @arr = (1, 2, 3);
  my $scalar = "@arr"; # $scalar contains '1:2:3'
}

As with any of Perl's special variables, it's always best to localise any changes within a code block.

Answer 3

You could also use join without any seperator

my $scalar = join( '' , @array ) ;

There is more than one way to do it.

Answer 4

in the spirit of TIMTOWTDI:

my $scal;
$scal .= $_ foreach @arr;

Answer 5

Read section Context in perldata . Perl has two major contexts: scalar and list.

For example:

@a = (1, 1, 1);   # list context
print @a;         # list context
$count = @a;      # scalar context, returns the number of elements in @a

etc.