From @LLFourn

my $a = "foo"; ($a if $a) = "bar"; say $a # bar

my $a = "foo"; ($a with $a) = "bar"; say $a # Cannot modify an immutable Str

my $a = "foo"; ($_ with $a) = "bar"; say $a # Cannot modify an immutable Str

From @zoffixznet

Changed it back to BUG based on discussion in http://irclog.perlgeek.de/perl6-dev/2016-09-22#i_13254335

From @LLFourn

20​:21 < llfourn_> m​: my $a = "foo"; ($a andthen $_) = "bar"; say $a
20​:21 < camelia> rakudo-moar e9409c​: OUTPUT«Cannot modify an immutable Str␤
in block <unit> at <tmp> line 1␤␤»

andthen also has the same behaviour.

On Fri, Aug 5, 2016 at 4​:53 PM Lloyd Fournier <perl6-bugs-followup@​perl.org>
wrote​:

# New Ticket Created by Lloyd Fournier
# Please include the string​: [perl #​128846]
# in the subject line of all future correspondence about this issue.
# <URL​: https://rt-archive.perl.org/perl6/Ticket/Display.html?id=128846 >

my $a = "foo"; ($a if $a) = "bar"; say $a # bar

my $a = "foo"; ($a with $a) = "bar"; say $a # Cannot modify an immutable
Str

my $a = "foo"; ($_ with $a) = "bar"; say $a # Cannot modify an immutable
Str