mixins – 为混合角色的属性赋值

我正在尝试使用 Enumeration role in Perl 6(作为修复文档问题 Enumeration role is not documented的一部分)的示例.我想出了这个简单的例子：

class DNA does Enumeration {
    my $DNAindex = 0;
    my %pairings = %( A => "T",T => "A",C => "G",G => "T" );

    method new( $base-pair where "A" | "C" | "G" | "T" )  {
        self.bless( key => $base-pair,value => %pairings{$base-pair},index => 33);
    }

    multi method gist(::?CLASS:D:) {
        return "$!key -> $!value with $!index";
    }

}

for <A C G T>.roll( 16 ) -> $letter {
    my DNA $base = DNA.new( $letter );
    say "Pairs ",$base.pair," with ",$base.gist;
}

从理论上讲,Enumeration有$！index,而index => 33我试着给它分配一个值;然而,它返回的就像是

Pairs T => A with T -> A with 0

任何其他方式直接为$！index分配一个值,我得到the “cannot assign to an immutable value我得到了另一个问题.根据one of the answers,这可能是一个错误;在这种情况下,我想知道是否有一些解决方法.

解决方法

这是一个错误 Cannot change native role attribute from consuming class(与您链接的答案中提到的错误无关).

我不知道一个解决方法.