Hi, the following is a source of a bug that took me awhile to figure out. 
use strict;

my $hash = undef;
print "shouldn't print\n" if $hash;      # prints nothing
print 1 if $hash->{1}; # should be a no-op, but it makes $hash to be {
+}
print "Still shouldn't print, but it does.\n"  if $hash;      # prints

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I thought a test such as "if $hash->{1}" wouldn't change $hash, but apparently it does. Is this a well-known behavior, and what's the reason for it? I fully appreciate that "$hash->{1} = 1;" would create the hash.

In reply to Why does testing a key create a hash? by johnnywang

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