Parameters — optional, default & slurpy

Required and optional positionals, default values, and slurpy @ / % catch-alls.

A signature's positional parameters are required by default. A ? makes one optional, an = value gives it a default, and a * makes it slurpy — absorbing all remaining arguments.

Default values #

A parameter with = expr uses that value when the argument is omitted.

sub g($x, $y = 10) {
    $x + $y;
}
say g(5);
say g(5, 1);

15
6

Optional parameters #

A trailing ? marks a parameter optional; when absent it is undefined, which .defined detects.

sub h($x, $y?) {
    $y.defined ?? "$x,$y" !! "$x only";
}
say h(1);
say h(1, 2);

1 only
1,2

Slurpy parameters #

A *@array parameter collects all remaining positional arguments into a list; *%hash does the same for named ones.

sub total(*@nums) {
    [+] @nums;
}
say total(1, 2, 3, 4);

10

Notes #

• Order matters: required positionals come first, then optional/defaulted ones, then the slurpy — which must be last among positionals.
• A defaulted parameter is implicitly optional; you rarely need both ? and =.
• The default expression can reference earlier parameters: sub f($x, $y = $x) {…}.