I fear it's the similar problem Perl6 has: add_topping runs push, but it doesn't change the array itself, so the isa check doesn't run.

It's also documented in MooX::HandlesVia:

methods delegated via the Moo handles interface are passed the attribue value directly. and there is no way to access the parent class. This means if an attribute is updated any triggers or type coercions WILL NOT fire.

map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

In reply to Re: Trouble or misunderstand of Types::Standard ArrayRef[elements] enforcement in Moo by choroba
in thread Trouble with, or misunderstanding of, Types::Standard ArrayRef[elements] enforcement in Moo by Your Mother

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