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Inheriting from Array: construction

There is an example:

class A is Array {
    has $.member = 42;
}
my $a = A.new: 1..10;
say $a.member; # OUTPUT: «(Any)␤»

Why doesn't it work? I also tried submethods TWEAK and BUILD, they also can't set a default value.

I found this workaround:

class A is Array {
    has $.member is rw;
    method new(|) {
        my $instance = callsame;
        $instance.member = 42;
        return $instance;
    }
}
my $a = A.new: 1..10;
say $a.member; # OUTPUT: «42␤»
Solution

  • Some core classes are currently not really set up to handle subclasses. Array being one of them. You've found one workaround. Another workaround (if you only need 1 additional attribute) is to use a role and does.

    role Member {
    has $.member is rw = 42
}
my @a does Member = 1..10;
say @a.member; # 42
my @b does Member(666) = 1..10;
say @b.member; # 666

    This should probably be made an issue