Details about ZeroCopyBuffer

[temeddix]

Hi, I have some new questions.

1. Can I make the function's return type to be something like ZeroCopyBuffer<MyCustomStruct>? Would this work as intended, without copying the fields of MyCustomStruct?

2. Is there a way to pass bytes to Dart, without letting go of the ownership in Rust? I wonder if there would be some data type like Arc, that can be used both in Dart and Rust, without any copying.

   pub fn my_function() -> Vec<u8> {
       let bytes = GLOBAL_HASHMAP.get("someKey").unwrap();
       bytes
   }

   In this case, we give away the ownership of bytes and are not able to access it anymore in Rust.

   pub fn my_function() -> ZeroCopyBuffer<Vec<u8>> {
       let bytes = GLOBAL_HASHMAP.get("someKey").unwrap();
       ZeroCopyBuffer(bytes)
   }

   Even if we use ZeroCopyBuffer, we cannot access that data in Rust anymore.

[fzyzcjy]

Can I make the function's return type to be something like ZeroCopyBuffer? Would this work as intended, without copying the fields of MyCustomStruct?

Yes and no.

ZeroCopyBuffer is implemented by Dart primitives, which only support a flat byte array.

But, if you generate some Dart code like:

class Apple {
  final Uint8List bytes;
  int get aaa => bytes[0] * 256 + bytes[1];
  int get bbb => bytes[2];
}

Then I guess it should work.

I wonder if there would be some data type like Arc, that can be used both in Dart and Rust, without any copying.

I am worried that this may violate the memory model of Rust very easily. For example, you can modify the bytes in Dart and Rust at the same time.

However, there can be fancier approaches.

Possibly related: #1132

[temeddix]

Okay, thank you very much for the help!

[fzyzcjy]

You are welcome!