$a[-1] is "the last element of @a". In the failure case, @a has no elements and so has no last element. I suppose you could argue that it should "create the last element". However, what would you have the following do?

my @a= ( 0, 1 );
$a[-1]= -1;    # @a is now ( 0, -1 )
$a[-2]= -2;    # @a is now ( -2, -1 )
$a[-3]= -3;    # fatal error
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Feel free to submit a patch that does unshift for that last line and that for my @a; $a[-100]= 1 produces @a= (1,(undef)x99). ;)

        - tye (but my friends call me "Tye")