Partial classes allow the implementation of a class to be split among multiple source code files in some object-oriented programming languages. The “partial” keyword denotes the chunks of the class, and all parts must have the same visibility. Advantages include organization and specialization, but they violate encapsulation principles.
A partial class is a feature in some object-oriented programming languages that allows the implementation of a class to be split up among multiple source code files. Partial classes, also called partial types, don’t exist in many programming languages, especially older ones like C++ and Java. Each language that implements partial classes, such as C# and Ruby, handles the implementation slightly differently.
In general, partial classes use the keyword “partial” to denote the chunks of the class, and whether the keyword is capitalized depends on the programming language used. Each part of the class is initialized the same way with identical class declarations and without these “partial” keywords, it would be illegal to create multiple classes in multiple files all with the same name. The “partial” keyword tells the compiler or interpreter, depending on the language, to merge all classes into one large unit. All distinct parts of the class must have the same visibility, public, private, or protected. If a part of the class is designated as abstract, the merged class is also designated as abstract, even if none of the other individual parts have been designated as such.
Implementing a partial class across multiple files has some significant advantages in both programming style and organization. Partial classes allow for the explicit separation of related pieces of code into more specialized groups. Also, a partial class allows multiple programmers to work on specific parts of the code without potentially breaking others and accidentally overwriting revisions. Even for individual programmers, partial classes can be useful as they can be used to create very large classes without creating even a single file that is bulky and difficult to organize and read.
Partial class implementation models also have some significant drawbacks. Despite being under the umbrella of object-oriented programming, partial classes actually violate the central encapsulation principles of object-oriented programming. In object-oriented programming, a class is assumed to be a single unified entity that has its own unique states and behaviors, is self-contained, and is capable of being used as a cohesive unit. Partial classes violate this idea because each partial class acts as a single separate class. Although the pieces that make up a partial class are merged into one large class at runtime, the pieces of the partial class are often independent entities that can be used on their own without requiring any form of merge.
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