Is it a bad practice to have multiple classes in the same file?

Question

I used to have one class for one file. For example car.cs has the class car. But as I program more classes, I would like to add them to the same file. For

Answer 1

I think you should try to keep your code to 1 class per file.

I suggest this because it will be easier to find your class later. Also, it will work better with your source control system (if a file changes, then you know that a particular class has changed).

The only time I think it's correct to use more than one class per file is when you are using internal classes... but internal classes are inside another class, and thus can be left inside the same file. The inner classes roles are strongly related to the outer classes, so placing them in the same file is fine.

Answer 2

No I don't think it's an entirely bad practice. What I mean by that is in general it's best to have a separate file per class, but there are definitely good exception cases where it's better to have a bunch of classes in one file. A good example of this is a group of Exception classes, if you have a few dozen of these for a given group does it really make sense to have separate a separate file for each two liner class? I would argue not. In this case having a group of exceptions in one class is much less cumbersome and simple IMHO.

Answer 3

I've found that whenever I try to combine multiple types into a single file, I always end going back and separating them simply because it makes them easier to find. Whenever I combine, there is always ultimately a moment where I'm trying to figure out wtf I defined type x.

So now, my personal rule is that each individual type (except maybe for child classes, by which a mean a class inside a class, not an inherited class) gets its own file.