For integers, it's no-op that evaluates its operand in scalar context. So, 
set_in_declare(~~@{$temp_name||[]});

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is being used in place of 
set_in_declare(scalar(@{$temp_name||[]}));

[download]

In reply to Re: The mystery of double bitwise negation by ikegami
in thread The mystery of double bitwise negation by hurricup

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