There's something fishy about $_. It's a TEMP with REFCNT=1. I believe that means it's a mortal. If so, that means noone claims a reference to $_, but first still uses it after the callback returns. This points to a bug in List::Util.

That said, the inplace lc($_)[1] should probably only happen in void context.

  1. This is the first I've ever heard about this!

In reply to Re^3: Strange behavior with List::Util qw{first} on perl >= 5.20 by ikegami
in thread Strange behavior with List::Util qw{first} on perl >= 5.20 by papioko

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