Perl Language Variables Scalar References
Example
A reference is a scalar variable (one prefixed by $ ) which “refers to” some other data.
my $value = "Hello";
my $reference = \$value;
print $value; # => Hello
print $reference; # => SCALAR(0x2683310)
To get the referred-to data, you de-reference it.
say ${$reference}; # Explicit prefix syntax
say $$reference; # The braces can be left out (confusing)
5.24.0
New postfix dereference syntax, available by default from v5.24
use v5.24;
say $reference->$*; # New postfix notation
This "de-referenced value" can then be changed like it was the original variable.
${$reference} =~ s/Hello/World/;
print ${$reference}; # => World
print $value; # => World
A reference is always truthy – even if the value it refers to is falsy (like 0 or "").
You may want a Scalar Reference If:
-
You want to pass a string to a function, and have it modify that string for you without it being a return value.
-
You wish to explicitly avoid Perl implicitly copying the contents of a large string at some point in your function passing ( especially relevant on older Perls without copy-on-write strings )
-
You wish to disambiguate string-like values with specific meaning, from strings that convey content, for example:
- Disambiguate a file name from file content
- Disambiguate returned content from a returned error string
-
You wish to implement a lightweight inside out object model, where objects handed to calling code don't carry user visible metadata:
our %objects; my $next_id = 0; sub new { my $object_id = $next_id++; $objects{ $object_id } = { ... }; # Assign data for object my $ref = \$object_id; return bless( $ref, "MyClass" ); }
