Inline code when counting data items (using templates)

There is a simple POD data type like

struct Item {
   int value1;
   double value2;
   bool value3;
}

Now I would like to write different count functions like it could be done with the following code (or some std method):

typedef bool Selector(const Item& i);
int count(const vector<Item>& items, Selector f) {
  int sum = 0;
  BOOST_FOREACH(const Item& i, items) {
    if(f(i)) {
      sum++;
    }
  }
  return sum;
}

with f e.g.

bool someSimpleSelector(const Item& i) {
  return i.value1 > 0; // quite simple criterion
}

However in this approach the compiler can not inline the function call and t开发者_运维技巧hus will not inline my (trivial) selection code.

My question would be: is there a possibility to implement the above code in a way, where the compiler can inline my selection code, but without implementing the whole count function again and again explicitely (for example by using templates)?

See the new boost range adaptors

Selector f;
int count = std::distance(items | boost::range::adaptor::filtered(f));

For more details read on. http://www.boost.org/doc/libs/1_43_0/libs/range/doc/html/range/reference/adaptors/reference/filtered.html

Replace the typedef with a template parameter, to allow generic functors:

template <typename Selector>
int count(const vector<Item>& items, const Selector &f)

Then replace your functions with function objects:

struct someSimpleSelector
{
    bool operator()(const Item& i) const { return i.value1 > 0; }
};

You should find that this gets inlined, with suitable compiler optimisation settings.

By the way, this particular problem can be solved using std::count_if().