Thanks moritz for the reply. I've already tried without 'is rw' and it works, and also I saw a spec. But, the question is why I see the same example in spec: 
Class traits are set using is:

    class MyStruct is rw {...}

[download]
and also see the same construction in wiki and it isn't work. You wrote:
(Update: it's an example in the spec, but I'm not sure what it means)
I think it means (from the spec):
If you declare the class as rw, then all the class's attributes default to rw, much like a C struct.

In reply to Re^2: Perl 6 class by Stanislav
in thread Perl 6 class by Stanislav

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