Arguments
The standard way of passing arguments is by position. The first argument passed in goes to the first parameter, the second to the second, and so on:
sub matchparams ($first, $second) { . . . } matchparams($one, $two); # $one is bound to $first # $two is bound to $second
Named Argument Passing
You can also pass arguments in by name, using a list of anonymous pairs. The key of each pair gives the parameter’s name and the value of the pair gives the value to be bound to the parameter. When passed by name, the arguments can come in any order. Optional parameters can be left out, even if they come in the middle of the parameter list. This is particularly useful for subroutines with a large number of optional parameters:
sub namedparams ($first, ?$second, ?$third is rw) { . . . } namedparams(third => 'Trillian', first => $name);
Sometimes the option syntax for pairs is clearer than the pair constructor syntax:
namedparams :third('Trillian'), :first($name);
Flattening Arguments
To get the Perl 5-style behavior where the elements of an array (or the pairs
of a hash) flatten out into the parameter list, use the flattening
operator in the call to the subroutine. Here,
$first
binds to @array[0]
and
$second
binds to @array[1]
:
sub flat ($first, $second) { . . . } flat(*@array);
A flattened hash argument acts as a list of pairs, which are bound to
the parameters just like ordinary named arguments. So,
$first
is bound to
%hash{'first'}
, and $second
is
bound to %hash{'second'}
:
sub flat_hash ...
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