... named captures ...

I think I would opt for a different course. Elaborating (well, second-guessing, really) on the example below, once you have validated a line , and given that the fields are completely mutually exclusive, the fields just pop out and go down as smoothly as oysters, with no capturing at all (update: no capturing to capture groups, that is).

c:\@Work\Perl\monks>perl -wMstrict -le
"use Regexp::Common;
 ;;
 my @lines = (
   'test1.cpp     0.00% of 21     0.00% of 16',
   'test2.c     None   16.53% of 484',
   'test3.h         0.00% of 138    None',
   '/x/y/foo.c      0.00% of 1    None',
   );
 ;;
 my $title   = qr{ \w+ (?: [.] \w+)* }xms;
 my $percent = qr{ $RE{num}{real} % \s+ of \s+ \d+ }xms;
 my $none    = qr{ None }xms;
 ;;
 for my $line (@lines) {
   print qq{line '$line'};
   die qq{  BAD LINE: '$line'} unless $line =~ m{
     \A $title (?: \s+ (?: $percent | $none)){2} \s* \z
     }xms;
   my ($t, $p1, $p2) = $line =~ m{ \A $title | $percent | $none }xmsg;
   print qq{  title: '$t'  pcent1: '$p1'  pcent2: '$p2'};
   }
"
line 'test1.cpp     0.00% of 21     0.00% of 16'
  title: 'test1.cpp'  pcent1: '0.00% of 21'  pcent2: '0.00% of 16'
line 'test2.c     None   16.53% of 484'
  title: 'test2.c'  pcent1: 'None'  pcent2: '16.53% of 484'
line 'test3.h         0.00% of 138    None'
  title: 'test3.h'  pcent1: '0.00% of 138'  pcent2: 'None'
line '/x/y/foo.c      0.00% of 1    None'
  BAD LINE: '/x/y/foo.c      0.00% of 1    None' at -e line 1.
[download]

Updates:

1. Actually removed capturing groups from validation regex.
2. It turns out the fields are not "completely mutually exclusive" as I originally claimed, so I had to change the extraction regex from
       m{ $title | $percent | $none }xmsg
   to
       m{ \A $title | $percent | $none }xmsg
   This somewhat vitiates the intended thrust of this post, but I think the main point stands. Oh, well...