In 5.10.0 and 5.10.1, $#a adds magic, so there's a performance penalty to $#a too. Either way, the cost has got to be minor.

Note that $#a only adds magic when $#a is used in an lvalue context in 5.12.

In reply to Re^4: How can I delete an element in a foreach cycle? by ikegami
in thread How can I delete an element in a foreach cycle? by saintex

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