Yes, we have it. This became the Proxy feature described under Lvalue routines in the design docs. They are already implemented in Rakudo, though I'll note there are some wrinkles as I mentioned in another comment I just posted to this thread. I hope to return to elaborate on Proxies in this thread in coming weeks/months.

In reply to Re^2: [perl6] Complex Attribute Validation and/or Triggers by raiph
in thread [perl6] Complex Attribute Validation and/or Triggers by duelafn

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