also support for fixed size arrays.

its quite common to have a struct with fixed sized arrays to pass around in C

We have asTypedList for exposing the native memory as a Dart array.

For structs with inline arrays:

struct MyStruct {
  uint8_t arr[10];
  int64_t arr2[3];
};

We need a dart syntax of representing an inline array.

We could opt for exposing this as a pointer, which provides [] and []= access.

class MyStruct extends Struct {
  @InlineArray(10)
  Pointer<Uint8> arr;

  @InlineArray(3)
  Pointer<Int64> arr2;
}

Using a Pointer as the representing type does not allow us to distinguish pointers and inline arrays by the Dart type. However, this is not really a problem since C does not support passing fixed-size arrays by value in calls.

cc @mkustermann

edit: We do not want to expose it as a pointer, rather as a CArray which represents a fixed-size inlined array.

class MS extends Struct {}

MS foo(MS ms); // C signature for passing struct by value.
@size(4)CArray<MS> foo(@size(4)CArray<MS> mss); // C signature for passing inline array of structs.
Pointer<MS> foo(Pointer<MS> ms); // C signature for passing pointer.

class MS2 extends Struct {
  MS ms; // Nested struct.
}
class MS3 extends Struct {
  @size(4)
  CArray<MS> mss; // Nested array of structs.
}
class MS4 extends Struct {
  Pointer<MS> mss; // Pointer to struct.
}

CArray would be a view on top of the underlying pointer (kind of like struct).

If we expose the nested structs and the inline array as getter/setter pair, the setters would do a memcopy of the whole underlying structure.

(As sidenote, we should also introduce memcopy on structs:

Pointer<MS> p1, p2;
p1.value = p2.ref; // Copies over all memory.

)

@dcharkes

I got this error when trying your solution to getting static arrays on Dart side

Code

class StaticArray extends Struct {
  @InlineArray(10)
  Pointer<Int32> array;
  @Int32()
  int len;
}

Result

$ dart structs.dart 
structs.dart:48:4: Error: Method not found: 'InlineArray'.
  @InlineArray(10)
   ^^^^^^^^^^^
structs.dart:129:15: Error: A function expression can't have a name.
  staticArray.forEach(idx, elem) => print("array[$idx]: $elem");
              ^^^^^^^
structs.dart:129:15: Error: Expected an identifier, but got 'forEach'.
  staticArray.forEach(idx, elem) => print("array[$idx]: $elem");
              ^^^^^^^

Does it mean that this is just a proposal?
What would be the canonical way of getting array data from FFI C pointers?
I'm referring to my latest question.

Thanks in advance!

Yes, for now it's just a proposal.

See the workaround made by @timsneath here for now.

I'll get around to implementing this in the future, I'm working on other dart:ffi features at the moment.