Perl6でコンストラクタでプライベートフィールドに値を渡したい

build.pl6

my class Hoge {
  has Str $!fuga;

  submethod BUILD(:$!fuga) {
  }

  method fuga {
    return $!fuga;
  }
}

my $hoge = Hoge.new(fuga => 'foo');
say $hoge.fuga; # foo

override_accessor.pl6

my class Hoge {
  has Str $.fuga;

  method fuga {
    die 'not accessible.';
  }

  method fugafuga {
    return $!fuga;
  }
}

my $hoge = Hoge.new(fuga => 'foo');
say $hoge.fugafuga; # foo
say $hoge.fuga; # not accessible.

private.pl6

my class Hoge {
  has Str $!fuga;

  method fuga {
    return $!fuga;
  }
}

my $hoge = Hoge.new(fuga => 'foo');
say $hoge.fuga; # (Str)

private_fail.pl6

my class Hoge {
  has Str $!fuga;

  method new(:$fuga) {
    return self.bless(:$fuga);
  }

  method fuga {
    return $!fuga;
  }
}

my $hoge = Hoge.new(fuga => 'foo');
say $hoge.fuga; # (Str)

private_success.pl6

my class Hoge {
  has Str $!fuga;

  method new(:$fuga) {
    my $self = self.bless;
    $self!fuga($fuga);
    return $self;
  }

  method fuga {
    return $!fuga;
  }

  method !fuga($fuga) {
    $!fuga = $fuga;
  }
}

my $hoge = Hoge.new(fuga => 'foo');
say $hoge.fuga; # foo
say $hoge!fuga('bar'); # syntax error

public.pl6

my class Hoge {
  has Str $.fuga;
}

my $hoge = Hoge.new(fuga => 'foo');
say $hoge.fuga; # foo