... you can't modify a list item in say a foreach loop ... but in the parameter list to a sub you can: $_[0] = 12 ...

Further to LanX's reply:   And, of course, one cannot modify a literal value in an argument list even though the list is passed as an array (of aliases). In no case can one modify a literal value: 1 is, let us fervently hope, always 1.

Win8 Strawberry 5.8.9.5 (32)  Tue 11/24/2020 14:56:16
C:\@Work\Perl\monks
>perl -Mstrict -Mwarnings -l
sub f { return $_[0] = 42; }

my $x = 88;
print f($x);
print   $x;

print f(99);
^Z
42
42
Modification of a read-only value attempted at - line 1.
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