簡単なキャッシュ

#include <iostream>
#include <string>
#include <sstream>
#include <map>

#ifdef _WIN32
#define _WIN32_WINNT 0x0501
#endif

#include <boost/asio.hpp>
#include <boost/timer.hpp>

using namespace std;

template <class I, class O>
class Cache {
  map<I, O> m_;
  O (*f_)(I x);
public:
  Cache(O (*f)(I x)): f_(f) {}

  O operator ()(I x) {
    map<I, O>::iterator i;
    i = m_.find(x);

    if (i != m_.end()) {
      return i->second;
    } else {
      O tmp = f_(x);
      m_.insert(pair<I, O>(x, tmp));
      return tmp;
    }
  }
};

namespace {
  string forecast(string query) {
    using namespace boost::asio;
    ip::tcp::iostream s("weather.livedoor.com", "http");

    s << "GET /forecast/webservice/rest/v1?" << query << " HTTP/1.1\r\n";
    s << "Host: weather.livedoor.com\r\n";
    s << "\r\n";
    s << flush;

    ostringstream out;
    string l;

    while (getline(s, l)) {
      out << l << endl;
    }

    return out.str();
  }
}

int main(int argc, char* argv[]) {
  Cache<string, string> proxy(forecast);

  boost::timer t;
  proxy("city=113&day=tomorrow");
  cout << "1: " << t.elapsed() << "s" << endl;

  t.restart();
  proxy("city=113&day=tomorrow");
  cout << "2: " << t.elapsed() << "s" << endl;

  t.restart();
  proxy("city=113&day=tomorrow");
  cout << "3: " << t.elapsed() << "s" << endl;

  return 0;
}

1: 2.219s

2: 0s

3: 0s