c# - One class per file rule in .NET?

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Top 5 Answer for c# - One class per file rule in .NET?

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I hate it when people think in absolutes and say you should never do this or that with something subjective and nit-picky like this, as if we all need to conform to someones stupid idea of right and wrong. Bottom line: having more than one class per file is totally fine if it makes sense. By makes sense I mean things like:

  1. Makes the code easier to digest and maintain
  2. Makes the solution less annoying (scrolling through countless unnecessary files) and less slow
  3. The dev team is okay with it as a local coding practice

A really good example of why I may want multiple classes per file:

Say I've got a few dozen custom exception classes, each one is a 4 liner, I could have a separate file for each one or I could group the exceptions and have a file per group. For me what seems the most rational/pragmatic approach is to group them, and just have a few files, because it's more efficient time/coding wise (I don't have to right-click -> Add Class, rename, 50 times), it keeps the solution less cluttered and better performing.

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One class per file also gives you a better idea of what each check in is changing without looking at the diffs of the file.

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static bool GeneralRuleShouldBeFollowed(IGeneralRule rule, IUseCase useCase) {     return (rule.Overhead(useCase)              < My.PersonalThresholds.ConformismVsPracticality); } 
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I sometimes group more than one class within a file if they are tightly coupled and at least one of them is very small.

General 'best practice' is to have one file per class.

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Beyond hypothetical arguments and focusing instead on Windows .NET with Visual Studio IDE and growing software projects, it just makes sense in this context to have one class per file.

In general, for visual reference nothing beats one class per file. Really.

I don't know if Microsoft does or doesn't do the same, however they did create the partial keyword to split one class over multiple files (this is even more severe). It's often used to split the auto-generated designer code from your custom code in the same class (but sometimes is used to allow different developers to work on the class at the same time via different files). So Microsoft does see benefits of multiple files and everybody has multiple file organization thoughts in mind for sure with .NET.

For nested classes you have no choice but to use one file, or at least the first parts of the classes in them. One file is necessary and fine in this case:

class BicycleWheel {     class WheelSpoke {     } } 

Otherwise why would you keep multiple classes in one file? The argument "because they're small" or associated with each other doesn't hold much water because eventually your classes will be associated with other classes. Ultimately you can't easily infer in-file organization of objects based on their usage especially as software continues to grow.

Additionally if you use folders for namespaces then you'll never have a class filename clash. It's also convenient to locate a class by filename on the file system when not inside a development environment like Visual Studio (e.g. if you want to quickly edit a class with Notepad or something quick/light).

So many good reasons...

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