What do delegates do in C#?

Question

Programming

I read about delegates, I realized that this is a type of object, like references to methods. But I still don't get it, for example:

long Sum(List<int> intList)
{
  long result = 0;
  intList.ForEach(delegate(int i) { result += i; });
  result result;
}

what is the delegate doing here?

Answer 1

Your task can be done in three ways:
1) create a method that will sum each element of the list into a variable, more precisely, into a class field.

long Result;
long Sum(List<int> intList)
{
    Result = 0;
    intList.ForEach(AddElement);
    return Result;
}

void AddElement(int i)
{
    Result += i;
}

2) In order not to create an "extra" function that is necessary only for a specific task, we can take an anonymous function. Anonymous functions in C# are used with delegates. Additionally, anonymous functions can use closures and there is no need to create an outer field.

long Sum(List<int> intList)
{
    long result = 0;
    intList.ForEach(delegate(int i) { result += i; });
    return result;
}

3) You can take a lambda - in this case, it's "syntactic sugar" - simplifying the creation of a delegate.

long Sum(List<int> intList)
{
    long result = 0;
    intList.ForEach(i => result += i);
    return result;
}

Answer 2

In this code, a delegate is passed inside the ForEach method, which is called for each element of the intList list. By code, it adds all the elements of the list to the result variable. For a specific problem, there are a dozen simpler and more reliable solutions, but this one looks like shit. Yes, delegates use to pass as a method parameter a reference to a method that satisfies the signature of the delegate.

Answer 3

In this case, sums the elements. Increments result by the current element from intList
UPD : in this case it is a reference to an anonymous method

Answer 4

Here is a good discussion on the subject.
Download Troelsen's textbook - he quite clearly explains everything in general)

Answer 5

functional object .
As you figure out what it is, you will understand what a delegate is.