Something that is just as fast (slightly faster) than use constant, that can be localized, and that is neat, is to create a reference or alias to a non modifiable variable.
in reply to Re: my $var; vs. use constant VAR = '';
in thread my $var = ''; vs. use constant VAR => '';
Try to modify it. You can't. Declare it at the top of your program and it is there for life. Put it in a sub and it stays around for the life of the sub.
See 75935 buried way at the bottom of this node.
local *CONST = \23.34234334234;
my @a=qw(random brilliant braindead); print $a[rand(@a)];