oop.p6

class A {
    has $.verbose;
    submethod BUILD (
        :$verbose
    ) {
    }
}

class B is A {
    has $.attr;
    submethod BUILD(
        :$attr
    ) {
    }
}

my $b = B.new(verbose => "dd", attr => "dddd");

say $b; # B.new(attr => Any, verbose => Any)

Remember that if you want it to populate the attributes, you need:

• to do the assignment in BUILD submethod's body:

class A {
    has $.verbose;
    submethod BUILD ( :$verbose ) {
        $!verbose = $verbose
    }
}

class B is A {
    has $.attr;
    submethod BUILD( :$attr ) {
        $!attr = $attr
    }
}

my $b = B.new(verbose => "dd", attr => "dddd");
say $b; # B.new(attr => "dddd", verbose => "dd")

• to specify it in the method's signature:

For the class A's BUILD, you could do :verbose($!verbose) right in the BUILD's signature. The same for B. But isn't :verbose($!verbose) too verbose? You can use :$!verbose instead. I guess that's probably what you meant but missed the elusive ! in the named parameter and that's why you got B.new(attr => Any, verbose => Any).

class A {
    has $.verbose;
    submethod BUILD( :!$verbose ) { }
}

class B is A {
    has $.attr;
    submethod BUILD( :!$attr ) { }
}

my $b = B.new(verbose => "dd", attr => "dddd");
say $b; # B.new(attr => "dd", verbose => "dddd")

Per the docs,

be careful when using this auto-binding of attributes when the attribute may have special type requirements... Remember, default values will be assigned unless you specifically take care of this attribute, and that default value will be Any, which would cause a type error.

I think the use of the BUILD submethod is also discouraged. Instead, you might want to use the TWEAK submethod.

Oooohh I see! Thanks a lot for taking the time with this! I really appreciate it :D.