What are Local Functions in C# 7.0?

The local function is an ability to declare methods inside an already defined function’s body. We are able to write local functions in C# 6.0 too but they can’t have a complete body or function name, and can only be anonymous.

Why Local Functions in C# 7.0?

As per the Microsoft blog, this is already (kind of) possible by using the Func and Action types with anonymous methods.



However, they lack a few features,

How to write Local Functions in C# 7.0

Local functions have the same capabilities as normal methods but will only be scoped to the block they were declared in.

Now, let’s try to write a normal local function first.

In the following image of code, you can check that I just created a function with two argument types (int, string) and it has all the behavior as a normal function. Since it is a local function, you can use or call it within the same function only.



Code

  1. static void Main(string[] args)
  2. {
  3. string myFunc(int p1,string p2)
  4. {
  5. return p2.Substring(p1);
  6. }
  8. Console.WriteLine(myFunc(2,"Nitin Pandit"));
  9. Console.Read();
  10. }
We can also use other properties of local function, like Generics, ref/out parameters, and params. So, let’s see how to use them.
  1. Local Generics Functions
    Local Generic function is really a nice property. It can be used in the same way as in a normal function and we can call it within the root function. In the following example, I have created myFunc as Generic.



    Code
    1. static void Main(string[] args)
    2. {
    3. void myFunc<T>(T value)
    4. {
    5. Console.WriteLine(value);
    6. }
    9. myFunc<string>("Nitin Pandit");
    10. Console.Read();
    11. }
  2. Using out/ref in Local Functions



    Code
    1. static void Main(string[] args)
    2. {
    3. void myFunc(int value1, out int value2)
    4. {
    5. value2 = value1 + value1;
    6. Console.WriteLine();
    7. }
    8. int i = 0;
    9. myFunc(12, out i);
    10. Console.WriteLine($"New Value of i : {i}");
    11. Console.Read();
    12. }
  3. Using params in Local Functions



    Code
    1. static void Main(string[] args)
    2. {
    3. void myFunc(params int[] items)
    4. {
    5. int res = 0;
    6. foreach (var item in items)
    7. {
    8. res += item;
    9. }
    10. Console.WriteLine($"Total : {res}");
    11. }
    13. myFunc(1,2,3,4,5,6,7,8,9);
    15. Console.Read();
    16. }

All these properties of local function make C# 7.0 more powerful. Thanks for reading this article. Stay tuned with us for more updates:

Connect (“Nitin Pandit”);