Allthough I originally wrote a module like Test::Warn, I wasn't aware of that behaviour. However perldiag describes it as a kind of optimization: 
Use of uninitialized value%s
  (W uninitialized) An undefined value was used as if it were already
  defined.  It was interpreted as a "" or a 0, but maybe it was a
  mistake.  To suppress this warning assign a defined value to your
  variables.

  To help you figure out what was undefined, perl will try to tell
  you the name of the variable (if any) that was undefined. In some
  cases it cannot do this, so it also tells you what operation you
  used the undefined value in.  Note, however, that perl optimizes
  your program and the operation displayed in the warning may not
  necessarily appear literally in your program.  For example, "that
  $foo" is usually optimized into ""that " . $foo", and the warning
  will refer to the "concatenation (.)" operator, even though there
  is no "." in your program.

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Greetings,
Janek

In reply to Re: Variable name missing in warning by bigj
in thread Variable name missing in warning by bogbert

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