After a hiatus in XML-land, I’m back developing in C++ land. We’ve moved to up Visual Studio 2010 since the last time I was doing serious development work, and so I’m getting to try out new new C++ language features. Today was my first foray into lambda expressions. Microsoft has some great examples in their documentation (Lambda Expression Syntax and Lambda Expressions in C++), but I need to do something quite common, but not in their list of examples.

My objective was to find a particular item in a collection matching some criteria. Essentially, it boils down to:

class ContainerClass {
   public:
      bool ItemExists(int itemId);
   private:
      struct Item{ int itemId; ... };
      std::vector<Item> _items;
};

I want to implement the ItemExists function. Without using lambda functions, you would iterate through the collection, checking for the matching itemId. How can we do this with lamba expressions?

bool ContainerClass::ItemExists(int itemId) {
   return std::find_if(_items.begin(), _items.end(), [itemId](const Item& item) { return item.itemId == itemId; }) != _items.end();
}

At this point, I’m not sure if this is a good or bad use of lambda expressions. Is the code more clear? What is the performance difference?