a generic buf eater

gistfile1.txt

my class Reader {
    my $.pos is rw = 0;
    my $.buf;

    method read(Buf $buf) {
        ...
    }

    method read-type(Any:U: $type) {
        my $width = nativesizeof($type);
        my $value = $!buf.subbuf($!pos, %type-widths{$type.perl});
        $!pos += $width;
        return $value;  # cast, but how?
    }
}