Investigate By-Ref Vector and Matrix Operators in C# 8.0

Summary

As mentioned in issue #598, the new in parameter keyword is allowed on operators and using literal values, so operator implementations can supersede the previous static by-ref operator alternatives.

Analysis

• Wait until the core has adopted C# 7.2.
• Make sure using the in keyword implicitly with non-referencable values (like literals or property return values) has no negative impact on performance. Read the docs, and if that’s not 100% clear, check out generated IL and x86 code in a sample project.
• Remove all static by-ref methods from Vector2/3/4, Quaternion and Matrix3/4 if they have an operator equivalent.
• Use the in keyword on parameters provided to the operators in question.

[Barsonax]

As a further enhancement one can add readonly to properties and methods etc now in C#8.0 to denote they do not change state: https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-8#readonly-members

(in C# 7.3 this was only possible on struct level)

This will enable the compiler to skip more defensive copies.

[Barsonax]

There are cases where defensive copies might occur when using the in keyword. This can reduce the performance. Making the struct readonly will prevent this.

https://blogs.msdn.microsoft.com/seteplia/2018/03/07/the-in-modifier-and-the-readonly-structs-in-c/

However since the X, Y etc fields are part of the public API its basically a breaking change.