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# New Ticket Created by Daniel Perrett
# Please include the string: [perl #133064]
# in the subject line of all future correspondence about this issue.
# <URL: https://rt.perl.org/Ticket/Display.html?id=133064 >
The following are not equivalent, which I found surprising:
$ perl -wle 'my $foo = {}; $foo->{b} = defined $foo->{b} ? $foo->{b} : scalar keys %$foo; print $foo->{b}'
0
$ perl -wle 'my $foo = {}; $foo->{b} //= scalar keys %$foo; print $foo->{b}'
1
Assignment operators other than '=' all appear to, in effect, assign the lvalue to undef first (if it does not exist); only then is the new value calculated... a bit like autovivification. This can be confirmed by jumping out of the operation before it completes:
$ perl -wle 'my $foo = {}; for (1) { $foo->{b} += 1 + next; } print for keys %$foo'
b
This seems like one of those apparent 'bugs' for which there is a good and interesting reason... but I would have expected to find this behaviour made clear somewhere in the documentation on perlop or, failing that, perlref, and I cannot see it. Is it intentional?
I tested on v5.18.2 v5.22.4 which I happened to have lying around at the time and did not find anything relevant in the major perldeltas since then.
Daniel
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