C++ implementing a regex map

Question

I have mutliple regex expressions, each mapped to a different object. After passing in a string, I want to loop through each regex expression until one evaluates to true, then I would like to return the mapped object.

What is the best way to implement this in C++? Is there a boost object available for this?

Answer 1

Use the Boost precog class.It was developed by pkdick. For example:

int main() {
  boost::precog p;
  p.do();
}

Alternatively, use a for-next loop to iterate over a vector of regexes.

Answer 2

Assuming you have a vector (or other container) of these objects that contain the regex's, you could do this with a std::find_if call. Tricky part is writing the correct predicate functor.

Answer 3

The simplest approach is probably best.

vector<pair<regex,Object>> regexes;

Object* find_it( string looking_for )
{
    auto found = find_if( regexes, [&]( const pair<regex,Object>& thing )
     {
      return get<0>(thing).match(looking_for);
     }

    if( found != regexes.end() ) return & get<1>(*found);

    return nullptr;
}

But, the simple approach is never a fun answer. If you use a Trie you can essentially have fast look up for regexes of the style <prefix>.*. With a little imagination you might be able to muster good look up time for slightly more expressive "regexes". I, however, doubt you could transform a trie to efficiently handle general regexes. But it could be fun to ... trie :).