Perl 6 and Parrot Essentials, Second Edition

Operators

Operators provide a simple syntax for manipulating values. A few characters take the place of a function call, or even several function calls. On the positive side this makes them incredibly convenient. On the negative side they’re also sometimes difficult to learn because they pack so much meaning into a small space. Many of the Perl 6 operators will be familiar, especially to Perl 5 programmers. The new operators either add new features to the language, or move Perl’s operator set toward a more consistent system.

Assignment and Binding

The = operator is for ordinary assignment. It creates a copy of the values on the righthand side and assigns them to the variables or data structures on the lefthand side:

$copy = $original;
@copies = @originals;

$copy and $original both have the same value, and @copies has a copy of every element in @originals.

The := operator is for binding assignment. Instead of copying the value from one variable or structure to the other, it creates an alias. An alias is an additional entry in the symbol table with a different name for the one container:

$a := $b;  # $a and $b are aliases
@c := @d;  # @c and @d are aliases

In this example, any change to $a also changes $b and vice versa, because they’re just two separate names for the same container. Binding assignment requires the same number of elements on both sides, so both of these would be an error:

# ($a, $b) := ($c);          # error
# ($a, $b) := ($c, $d, $e);  # error

The ::= operator is a variant ...