C# 7.0 – #4. Local functions

In C# 6.0 there is no way to declare a function which is local to another function, that is a function visible only inside the body in which is declared. The best way to accomplish this is to declare a delegate variable of type Func<T1,TResult> (or one of the several overloads available), ad then use anonymous methods or lambda expression to write the code of the function, as shown here.

// c# 6.0
Func<int, int, int> sum = (k, y) => {
      return k + y;

int c = sum(a, b);

This is not an optimal way to use local function, because of some limitations.

C# 7.0 comes with a true local function, and overcomes all the previous limitations.

Here is an example:

int DoSum(int a, int b)
   return LocalSum(a, b);

   int LocalSum(int x, int y)
      return x + y;

This is a more natural way to declare and use a local function.