Can we implement ANSI C's `offsetof` in Delphi?

Question

For reference: The offsetof macro(!) takes a struct data type and a member of the specified struct as arguments and returns an integer offset of the given member relative to the beginning of the struct. See the detailed overview and references.

The logic behind the generic offsetof is quite simple and can be reproduced in Delphi with ease (more or less) (literally with ease, elimination of predeclared pointer type requirement makes it a basic inline expression, see David Heffernan's answer and comment about swapping reference and dereference operators) as in-place code. However, I see absolutely no way to convert the in-place code solution to the reusable function. Can we actually do that?

Answer 1

Without a pre-processor or a built-in function, there's no way to do it quite as cleanly as the offsetof macro. The way that offsetof is able to do it so cleanly is that the pre-processor does the work. In fact some compilers implement it as a built-in, but that's beside the point. Delphi has no pre-processor, and no built-in offsetof.

The cleanest solution I know is like this:

NativeUInt(@TMyRecord(nil^).MyField)

But that is nothing like as clean as

offsetof(struct MyStruct, MyField)