What is so special about closures?

Question

I\'ve been reading this article about closures in which they say:

• \"all the plumbing is automatic\"
• the compiler \"creates a wrapper class\" and \"extends

Answer 1

Your example isn't clear, and doesn't (IMO) show typical capture usage (the only thing captured is a, which is always 3, so not very interesting).

Consider this text-book example (a predicate):

List people = ...
string nameToFind = ...
Person found = people.Find(person => person.Name == nameToFind);

Now try it without a closure; you need to do a lot more work, even if we are lazy:

PersonFinder finder = new PersonFinder();
finder.nameToFind = ...
Person found = people.Find(finder.IsMatch);
...
class PersonFinder {
    public string nameToFind; // a public field to mirror the C# capture
    public bool IsMatch(Person person) {
        return person.Name == nameToFind;
    }
}

The capture approach extends further to lots of variables at different scopes - a lot of complexity that is hidden.

Other than the names, the above is an approximation of what the C# compiler does behind the scenes. Note that when additional scopes are involved we start chaining the different capture classes (i.e. inner scopes have a reference to the capture class of outer scopes). Quite complex.

Jon Skeet has a good article on this here, and more in his book.