trait is rw

Documentation for trait is rw assembled from the following types:

language documentation Type system

From Type system

(Type system) trait is rw

Defined as:

sub trait_mod:<is>(Mu:U $type:$rw!)

The trait is rw on a class will create writable accessor methods on all public attributes of that class.

class C is rw {
    has $.a;
my $c = = 42;
say $c# OUTPUT: «42␤»

class Routine

From Routine

(Routine) trait is rw

multi sub trait_mod:<is>(Routine $r:$rw!)

When a routine is modified with this trait, its return value will be writable. This is useful when returning variables or writable elements of hashes or arrays, for example:

sub walk(\thing*@keysis rw {
    my $current := thing;
    for @keys -> $k {
        if $k ~~ Int {
            $current := $current[$k];
        else {
            $current := $current{$k};
my %hash;
walk(%hash'some''key'12= 'autovivified';
say %hash.perl;


("some" => {"key" => [Any, [AnyAny"autovivified"]]}).hash

Note that return marks return values as read only; if you need an early exit from an is rw routine, you have to use return-rw instead.