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As you indicate, you're throwing away the possibility of value validation.
As I indicate, Attribute::Property takes that argument away. You may not like that it is implemented as an attribute, but never did I say that lvalues imply throwing away the possibility of value validation. If anything, I said that it used to be harder without A::P. As with any lvalue in Perl: you can validate it as long as you don't fear tie. For $foo this hasn't been a problem, but for $object->foo some people do object.
I have yet to see code like this. And fortunately so.
Saying that you can use attributes to get value validation back doesn't comfort me.
If this is indeed because of CHECK, I'll be happy to add another module, one that does the same thing without attribute syntax1. Attribute syntax isn't needed, it's just very nice syntactic sugar that doesn't require a source filter. But for some reason, I do not think this is the real reason for you not to use this lvalue properties.
I hope that you just object to tie, or to anything that disagrees with perldoc, or to "experimental" features, because Perl 6 will assume you want lvalue accessors.
I really like Ruby's compromise.
So do I.
However in Perl I'll continue to use rvalue accessors, thankyouverymuch.
Don't let my advocacy for laziness stop you.