An alternate to option 2, slightly faster: 
use strict;
use Benchmark qw/cmpthese/;
my $p = 'stringwithnospacesinit';
my ($a,$b);
cmpthese(
  -5,
  {
    a => sub{
      $a = $p;
      $a =~ s/(.)/$1\\s*/g;
    },
    b => sub{
      $b = $p;
      $b = join('\s*',split(//,$b));
    },
  }
);
__END__
     Rate    a    b
a 62530/s   -- -20%
b 78403/s  25%   --

[download]
update - typo fix

In reply to Re^4: Generalising string in pattern by keszler
in thread Generalising string in pattern by rajyalakshmi

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