Re: find regex in backward direction ?

[kdevel via Digitalmars-d-learn]

On Saturday, 19 December 2020 at 12:52:54 UTC, Виталий Фадеев 
wrote:
Goal:
    size_t pos = findRegexBackward( r"abc"d );
    assert( pos == 4 );


module LastOccurrence;

size_t findRegexBackward_1 (dstring s, dstring pattern)
{
   import std.regex : matchAll;
   auto results = matchAll (s, pattern);
   if (results.empty)
      throw new Exception ("could not match");
   size_t siz;
   foreach (rm; results)
      siz = rm.pre.length;
   return siz;
}

size_t findRegexBackward_2 (dstring s, dstring pattern)
// this does not work with irreversible patterns ...
{
   import std.regex : matchFirst;
   import std.array : array;
   import std.range: retro;
   auto result = matchFirst (s.retro.array, pattern.retro.array);
   if (result.empty)
      throw new Exception ("could not match");
   return result.post.length;
}

unittest {
   import std.exception : assertThrown;
   static foreach (f; [&findRegexBackward_1, 
&findRegexBackward_2]) {
      assert (f ("abc3abc7", r""d) == 8);
      assert (f ("abc3abc7", r"abc"d) == 4);
      assertThrown (f ("abc3abc7", r"abx"d));
      assert (f ("abababababab", r"ab"d) == 10);
   }
}