use strict;
use warnings;
use v5.10;

our $_cached;
sub somefunc
{
   $_cached //= do {
     say "Heavy calculations";
     42+($ARGV[0]||0);
   };
}

say somefunc();
say somefunc();
__END__
Heavy calculations
42
42

##</code><code>##

use strict;
use warnings;
use v5.10;

sub somefunc
{
   state $var = do {
     say "Heavy calculations";
     42+($ARGV[0]||0);
   };
}

say somefunc();
say somefunc();
__END__
Heavy calculations
42
42

##</code><code>##

{
  local $_cached = undef;
  local @ARGV = (3);
  say somefunc();
}
{
  local $_cached = undef;
  local @ARGV = (5);
  say somefunc();
}