dart:ffi remove Pointer.offsetBy

[dcharkes]

C++ uses the size of the type when doing pointer arithmetic, we support this with Pointer.elementAt(). It only works for Pointer<T> where T has a size. This is the preferred way of using an array of elements.

Pointer.offsetBy() enables taking arbitrary offsets (in bytes) on any Pointer. This is not the preferred way, possibly we can leave it out completely.

[sjindel-google]

We will remove it.

[dcharkes]

We'll change offsetBy to _offsetBy after the Structs API revamp has landed (it's references in the frontend, so it will conflict when changed).

[sjindel-google]

What was the reasoning to remove it?

[dcharkes]

I think the reasoning was that using offsetBy is error-prone (creating unaligned pointers). If people wanted to do that, they should explicitly convert to Pointer<Uint8> with casting, do the pointer arithmetic, and cast back to the original pointer.

We could even provide that in package:ffi as an add on (which users would import manually):

extension PointerArithmetic<T extends NativeType> on Pointer<T> {
  Pointer<T> offsetBy(int numBytes) => cast<Uint8>().elementAt(numBytes).cast();
}

[dcharkes]

We'll remove it for now.