Let's look at the following Example:
We can see that in this code the
Main() method has another declared method
Result(). This nested method is called local function and is an innovation in C# 7.
Local functions can be declared inside every other method. When the C# compiler compiles such functions they are turned into private methods. Because you will learn about the difference between
private methods later, we can now say that
private can be used only in the class, in which they have been declared. The programs which we write at this level are using only one class, therefore we can say that we can use nested methods without any concerns.
With time and practice you will see that when you are writing code, you often need methods that you only need once, or the method we need gets very long. We said earlier that when a method contains too many lines of code it becomes hard to read and maintain.
This is where local functions come to help - they help us to declare a new method in another one we already have, and it will be used only once. This helps our code to be ordered better and easier to read, which helps for faster correction if there is an error in the code and limits the possibility for mistakes when making changes in the program logic.
Let's look again the above example.
In this example the
Result() method is a local function, because it is nested in the
Main() method, i.e.
Result() is local for
Main(). This means that the
Result() method can only be used in the
Main() method, because it's declared inside it. The only difference between nested and normal methods is that nested methods can't be
static. Because the definition for
static will be seen later, we will say for the moment that when declaring a local function we write only the return value type, the name of the method and its list of parameters. In this case this is
double Result(double a, double b).
Local functions can access variables, which are in the method containing them. The next example demonstrates how this is happening.
This feature of nested methods makes them very helpful when solving a problem. They save time and code, which we would otherwise lose to give them parameters and variables, which we can already use in nested methods.