Assigning to C<$#days> actually changes the length of the array.
Shortening an array this way destroys intervening values. Lengthening
an array that was previously shortened does not recover values
-that were in those elements. (It used to do so in Perl 4, but we
-had to break this to make sure destructors were called when expected.)
+that were in those elements.
X<$#> X<array, length>
You can also gain some minuscule measure of efficiency by pre-extending