Understanding the 'internal' Keyword in C#

C# internal Keyword

The internal keyword is an access modifier used to control the visibility and accessibility of classes, methods, properties, and other members within the same assembly (project). It restricts access to elements within the boundaries of the current assembly, making them inaccessible from outside assemblies.

Usage of the internal keyword:

// File 1: ClassA.cs
using System;

internal class ClassA
{
    internal void InternalMethod()
    {
        Console.WriteLine("This method can be accessed within the same assembly.");
    }
}

In this example, ClassA is marked as internal, and its method InternalMethod is also marked as internal. This means that both the class and the method can only be accessed by other classes within the same assembly (project).

Key points to note about internal:

1. The internal keyword is useful when you want to hide implementation details and ensure that certain classes or members are not accessible from outside the assembly.

2. Elements marked as internal can be freely used and accessed by other classes within the same assembly but not by classes in different assemblies.

3. By default, if you don't specify an access modifier for a class or a member, it is considered internal.

Here's an example of using the internal keyword:

// File 2: Program.cs
using System;

public class Program
{
    static void Main()
    {
        ClassA objA = new ClassA();
        objA.InternalMethod(); // This method can be called as both classes are in the same assembly.
    }
}

In this example, Program is a different class in a different file but within the same assembly as ClassA. Therefore, it can access the InternalMethod of ClassA.

Using the internal keyword allows you to control the visibility of classes and members, ensuring that certain elements are not exposed to external assemblies and promoting a more controlled and modular codebase.