#!/usr/bin/perl
use strict;
use warnings;

my @strings = ( 
     '1. Foo::Bar', 
     '2. Foo::Bar(', 
     '3. Foo::Bar  (', 
     '4. Foo::Bar '
   );

for ( @strings ) {
  print $_,$/ if /\w+::(?>\w+)(?!\s*\()/;
}
__END__
1. Foo::Bar
4. Foo::Bar