What is the purpose of using the “partial” keyword in c#?

In C#, the `partial` keyword is used to indicate that a class, structure, or interface can be defined in multiple source files. Using the `partial` keyword allows the definition of a type to be split into multiple parts, each of which can be defined in different source files.

Partial serves a few functions:

1. Improving code readability and maintainability by breaking down a type definition into multiple sections can make the code clearer and easier to understand. Each section can be responsible for different functionalities or features, reducing complexity and coupling. Each section can be defined in independent files, making it easier to organize and manage the code.
2. Support adding custom code in auto-generated code: When using code generation tools to generate code, the generated code is usually defined using the partial keyword. By adding custom code in another section, you can avoid modifying the generated code, reducing the risk of losing custom code when regenerating the code.
3. Support for partial implementation of class extension: using the `partial` keyword allows for the addition of new functionalities or features to a class without modifying the original class. This is particularly useful when using third-party libraries or frameworks, as it allows for extending existing classes by defining extension methods or properties in another section.

It is important to note that the “partial” keyword can only be used in the definition of classes, structures, and interfaces, and not in the definition of methods, properties, or events. All parts of the same type must have the same access modifier, otherwise it will result in a compilation error.