I'd prefer not supporting applying local to :lvalue subs over requiring them to return an lvalue.
Requiring that a second routine be written in order to even look at the rvalue is ugly. But even uglier is forcing all such 'set this' operations to create an lvalue.
Consider an object that interfaces to some 'thing' outside the process.
99% of the time, when someone writes $obj->Prop= $value; they won't be using local with it. But the design requires that even in those 99% of cases, the 'set' method must not only create a dummy variable, but it must query the external 'thing' to initialize this dummy lvalue just in case local is being used.
I'd like to be able to write lvalue-only methods. And I'd like to write 'set' methods that don't directly store their rvalue argument(s) anywhere.
I like the blurring of methods and member variables, so I don't mind that someone might try to use my lvalue-only method in a non-assignment scenario. I'd just throw an exception for such. So $obj->Prop= $value; can return $value even if $obj has no way to query the external 'thing' to ask it what its Prop currently is. So writing $value= $obj->Prop; can throw an exception.
So I think local should produce code nearly identical to:
and support local well w/o forcing the "return an lvalue" design which has preventing from ever want to use :lvalue in Perl5 and sounds like it will do that same for me in Perl6.