But

> Consider the relative difficulty of fixing your problem case vs. my counter-factual problem case:

while(  $x  = shift @a ) {    # Fixed

this is not a fix because while stops, if any element of @a is false.

  DB<187> @a=(1,undef,2,3,0,4,5)

  DB<188> print $x while $x =shift @a
1
  DB<189> print $x while $x =shift @a
23
  DB<190> print $x while $x =shift @a
45
  DB<191> print $x while $x =shift @a
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Thats the old semipredicate problem, which can only be solved with list-assignments.¹

But I agree with you that it's most probably too late to fix that design decision...

¹) for completeness: no defined doesn't help here, if undef is a legal value.

updates

• corrected "semipredicate problem"
• improved code example
• your "better" update is indeed better

²) best answer so far