Using in instead of ref?

[Happypig375]

There are many const T* parameters in Box2D. The easy way is to treat all of them as ref, i.e. not caring about the const part. However, this not only causes unnecessary friction when using the methods, such as the need to declare parameters on a separate line (you can just supply a value to an in parameter), but also loses the readonly intention of the pointer. It may be more correct to expose these pointers as in instead of ref.

Documentation on in vs ref: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/method-parameters#reference-parameters

[Happypig375]

Since you translate constant struct pointers that have an associated count to ReadOnlySpan instead of Span, constant struct pointers that only point to one item should be translated as in instead of ref too.

[ikpil]

Sorry for the late reply.
I completely agree with what you mentioned.
I’ll make the changes that can be adjusted accordingly.

[Happypig375]

It seems that some functions that only take readonly parameters, like b2CollideCircles are now a mix of in and ref, which is weird. I thought that const T* meant in and regular parameters stay as regular parameters.

Box2D.NET/src/Box2D.NET/B2Manifolds.cs

Line 45 in 31376f3

public static B2Manifold b2CollideCircles(ref B2Circle circleA, in B2Transform xfA, ref B2Circle circleB, in B2Transform xfB)

[Happypig375]

So inconsistent... Some Id parameters use in and others not. Do you really need to pass a B2ShapeId which is the size of a long by ref? The resulting size is the same on 64-bit operating systems but now you have indirection.

[ikpil]

Thank you for letting me know. If anything is missing, please let me know. I will review it and make the necessary updates.

• Refactor: Use 'in' modifier for B2Circle parameters #84

[ikpil]

#85

[Happypig375]

It is also for B2Polygon in B2Manifolds.cs.

[ikpil]

I applied this change, but I’m getting a compiler warning.
The issue occurs when accessing an internal array from a readonly struct passed with in.

Although the struct is treated as readonly, arrays are reference types and their elements remain mutable, which causes the compiler warning.