[perl #123835] Cannot use 'is rw' on optional parameter

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# New Ticket Created by  Adrian Kreher 
# Please include the string:  [perl #123835]
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# <URL: https://rt.perl.org/Ticket/Display.html?id=123835 >


I tried 'sub f($x is rw = 60)', STD parses it but rakudo prohibits it.
'is copy' works. I don't see any obvious reason why it shouldn't work.

This is perl6 version 2015.01-141-gfec2339 built on MoarVM version
2015.01-34-g2d7eddb

143936       avuserow | m: sub f($x is rw = 60) {$x++; say $x}; f
143937       +camelia | rakudo-moar 949b80:
OUTPUT«?31m===?0mSORRY!?31m===?0m Error while compiling
/tmp/L9ZwKOd6I3␤Cannot use 'is rw' on an optional parameter␤at
/tmp/L9ZwKOd6I3:1␤------> ␤»
144045       avuserow | std: sub f($x is rw = 60) {$x++; say $x}; f
144046       +camelia | std f9b7f55: OUTPUT«ok 00:00 140m␤»
144058       avuserow | rakudobug?
144141          masak | no, I don't think so.
144149          masak | or, hm.
144210          masak | I don't immediately see what the problem is with
using 'is rw' on an optional parameter...
144227          masak | sometimes it doesn't bind with the outside, but
that's not a show-stopper.
144253          masak | avuserow: please submit it and we can have a
discussion of why it should or should not be possible ;)


In the "Parameter traits" section of S06, it mentions about 'is rw' and
defaults, saying this should be allowed in some cases. But I'm not sure
if that applies to this case or not.