Are streams zero-copy?

[patmuk]

I recall that sending data from Rust to Dart is not zero-copy due to limitations in FFI.
And there is a cheap way to do so: Using RustAutoOpaque, which is basically an Arc, can make a cheap clone on the reference and send that to the dart side. This is actually what I am doing, and I will most probably not change that :)

However, out of curiosity: When I am using a stream - is the data sent copied?

Imagine I have

pub struct WholeAppState {
    pub something_big: Vec<HeavyBinary>,
}
pub type HeavyBinary: Vec<u8>

If I have a function, like the time example where I update some items of the something_big vector, will every time the whole vector be copied through the stream?

[fzyzcjy]

sending data from Rust to Dart is not zero-copy

It seems that Rust -> Dart is zero copy, but Dart -> Rust is not (yet). https://cjycode.com/flutter_rust_bridge/guides/types/translatable/zero-copy

When I am using a stream

Streams and function return values use the same underlying mechanism.

[patmuk]

Ah, thanks! Oh, streams are even mentioned in the linked documentation.

[fzyzcjy]

You are welcome!