[ppog]

Your comment about changing a field to a property being a breaking change in C# is correct, but in practice, C# programmers tend to use auto properties (e.g. public int Left { get; private set; }) rather than public fields. These are fully fledged properties, but the getters and setters are implemented by the compiler (and back directly onto a compiler-generated field). Because they are properties, they can then be changed to computed properties (or e.g. validation added to setters) without breaking binary or reflection compatibility.