reference-types VS gc

> It could be an interesting use case for WASM if the problem of passing data into the WASM VM cheaply (perhaps by reference) can be solved.

WASM Reference Types should hopefully solve this. The WASM working group seems to have some good momentum - so I'm hopeful this (or a similar replacement spec) will land sooner rather than later.

https://github.com/WebAssembly/reference-types/blob/master/p...

AFAIK GC is irrelevant for "direct DOM access", you would rather want to hop into the following rabbit hole:

- reference types: https://github.com/WebAssembly/reference-types/blob/master/p...

- interface types (inactive): https://github.com/WebAssembly/interface-types/blob/main/pro...

- component model: https://github.com/WebAssembly/component-model

If this looks like a mess, that's because it is. Compared to that, the current solution to go through a Javascript shim doesn't look too bad IMHO.

[1]: https://github.com/WebAssembly/proposals

A glance of the overview and spec seems to indicate that WASM will provide some primitive data types, and any GC language can build their implementation on top of it. As I understand it, it's heavily based on Reference Types[3], which allows acting on host-provided types, and is already considered part of the spec [4]. It doesn't remove the need for the 5 different runtimes to have their own GC, but it lowers the bulk that the runtimes need to carry around, and offloads some of that onto the WASM runtime instead.

[3]: https://github.com/WebAssembly/reference-types/blob/master/p...

They've talked about interface types, and added reference types, which is a stepping stone toward the GC extension proposal, which would be a stepping stone toward manipulating the DOM from the WebAssembly side, but their official roadmap page is more short-term.

Nope, WASM reference types, it has nothing to do with .NET type system.

> And there's been talk of exposing the JS GC to wasm for a few years. Hopefully when that stuff lands, it'll get easier to marshal objects across the gap.

You don't need a Wasm GC to do this. If you only need js objects to pass on to, say, the host's function or check is null or not, then reference types that are opaque external references: https://github.com/WebAssembly/reference-types/blob/master/p...

You can even do many more things if you export `Reflect` to WebAssembly: https://github.com/AssemblyScript/assemblyscript/blob/main/t...

Reference Types are available almost everywhere already (In Safari will be available after 15.0): https://webassembly.org/roadmap

Re: GC -- yes, indeed, the whole business with safepoints arose from the need to support Wasm reference types as a backend for Wasmtime or Firefox. No safepoints are needed for Rust (or other C-like) code.

Reference Types,

It may take some time for WasmGC to be usable by .NET. Based on the discussions the first version of WasmGC does not have a good way to handle a few .NET specific scenarios, and said scenarios are "post-post-mvp". [0]

My concern, of course, is that there is not much incentive for those features to be added if .NET is the only platform that needs them... at that point having a form of 'include' (to where a specific GC version can just be cached and loaded by another WASM assembly) would be more useful, despite the pain it would create.

[0] - https://github.com/WebAssembly/gc/issues/77

Yes, that's definitely true: a single GC will not be optimal for everything, or even possible. Atm interior pointers are not supported at all, for example, but they are on the roadmap for later:

https://github.com/WebAssembly/gc/blob/main/proposals/gc/Pos...

What launched now is enough WasmGC to support a big and useful set of languages (Java, Kotlin, Dart, OCaml, Scheme), but a lot more work will be required here!

GC proposal is from 2018: https://github.com/WebAssembly/proposals/issues/16 and there’s code: https://github.com/WebAssembly/gc/blob/master/proposals/gc/O...

Seems like an awefully long time for progress to be made, given all the possibilities it would unlock.

First is the size. Writing a server-side and client-side program is possible with Rust, and the resulting WASM package will be small enough. At the same time, Microsoft Blazor converts C# code to WASM, but the client delivery has to include the reduced .NET runtime, taking several megabytes for a script. The same is true for GoLang, even with an attempt to reduce the runtime delivery in TinyGo WASM. Developers want to work with their favorite languages, whether it is Java, Kotlin, Dart, C#, F#, Swift, Ruby, Python, C, C++, GoLang, or Rust. These languages produce groups of runtimes. For example, JVM and .NET have many common parts, Ruby and Python are dynamically interpreted at runtime, and all mentioned depend on automatic garbage collection. For smaller WASM packages, browser vendors can include extended runtime implementations, for example, by delivering a general garbage collector as part of WASM. Garbage collection support by WASM is currently in progress: WASM GC, .NET WASM Notes.

My understanding is that the main limitation is technical. WASM doens't do GC or the host system calling conventions and cannot interact directly with object from Javascript because of this. However, this is being worked[0] on and will be solved eventually. Even without this the performance overhead of bridging to JS is low enough that WASM frameworks can beat out React.

0: https://github.com/WebAssembly/gc/blob/main/proposals/gc/Ove...

I’ve just watched a video on YouTube from Google I/O 2023 on Flutter for the web. Kevin Moore explains that Flutter can compile to Wasm, but now that GC support has been added to the standard and WasmGC is supported in Chromium and Firefox, I’m quite intrigued.

I have found the main thread about using WebAssembly GC in C#: https://github.com/WebAssembly/gc/issues/77. If I understand it correctly, it is not possible to use the current prototype version of GC in C#.

The .net team has given their notes on it, the concern is more on the memory layout from what I remember. Though it may be possible still. The runtime would likely still ship some gc code, but only a subset for cases not supported by the wasm gc itself and a few more for interfacing with the gc service, which overall should still result on smaller payloads compared to current sizes.

I assume that's one of the parts of the work done at https://github.com/WebAssembly/gc - not happening any soon yet, but it'll eventually be done.