bevy/benches
Gino Valente 59c0521690
bevy_reflect: Add Function trait (#15205)
# Objective

While #13152 added function reflection, it didn't really make functions
reflectable. Instead, it made it so that they can be called with
reflected arguments and return reflected data. But functions themselves
cannot be reflected.

In other words, we can't go from `DynamicFunction` to `dyn
PartialReflect`.

## Solution

Allow `DynamicFunction` to actually be reflected.

This PR adds the `Function` reflection subtrait (and corresponding
`ReflectRef`, `ReflectKind`, etc.). With this new trait, we're able to
implement `PartialReflect` on `DynamicFunction`.

### Implementors

`Function` is currently only implemented for `DynamicFunction<'static>`.
This is because we can't implement it generically over all
functions—even those that implement `IntoFunction`.

What about `DynamicFunctionMut`? Well, this PR does **not** implement
`Function` for `DynamicFunctionMut`.

The reasons for this are a little complicated, but it boils down to
mutability. `DynamicFunctionMut` requires `&mut self` to be invoked
since it wraps a `FnMut`. However, we can't really model this well with
`Function`. And if we make `DynamicFunctionMut` wrap its internal
`FnMut` in a `Mutex` to allow for `&self` invocations, then we run into
either concurrency issues or recursion issues (or, in the worst case,
both).

So for the time-being, we won't implement `Function` for
`DynamicFunctionMut`. It will be better to evaluate it on its own. And
we may even consider the possibility of removing it altogether if it
adds too much complexity to the crate.

### Dynamic vs Concrete

One of the issues with `DynamicFunction` is the fact that it's both a
dynamic representation (like `DynamicStruct` or `DynamicList`) and the
only way to represent a function.

Because of this, it's in a weird middle ground where we can't easily
implement full-on `Reflect`. That would require `Typed`, but what static
`TypeInfo` could it provide? Just that it's a `DynamicFunction`? None of
the other dynamic types implement `Typed`.

However, by not implementing `Reflect`, we lose the ability to downcast
back to our `DynamicStruct`. Our only option is to call
`Function::clone_dynamic`, which clones the data rather than by simply
downcasting. This works in favor of the `PartialReflect::try_apply`
implementation since it would have to clone anyways, but is definitely
not ideal. This is also the reason I had to add `Debug` as a supertrait
on `Function`.

For now, this PR chooses not to implement `Reflect` for
`DynamicFunction`. We may want to explore this in a followup PR (or even
this one if people feel strongly that it's strictly required).

The same is true for `FromReflect`. We may decide to add an
implementation there as well, but it's likely out-of-scope of this PR.

## Testing

You can test locally by running:

```
cargo test --package bevy_reflect --all-features
```

---

## Showcase

You can now pass around a `DynamicFunction` as a `dyn PartialReflect`!
This also means you can use it as a field on a reflected type without
having to ignore it (though you do need to opt out of `FromReflect`).

```rust
#[derive(Reflect)]
#[reflect(from_reflect = false)]
struct ClickEvent {
    callback: DynamicFunction<'static>,
}

let event: Box<dyn Struct> = Box::new(ClickEvent {
    callback: (|| println!("Clicked!")).into_function(),
});

// We can access our `DynamicFunction` as a `dyn PartialReflect`
let callback: &dyn PartialReflect = event.field("callback").unwrap();

// And access function-related methods via the new `Function` trait
let ReflectRef::Function(callback) = callback.reflect_ref() else {
    unreachable!()
};

// Including calling the function
callback.reflect_call(ArgList::new()).unwrap(); // Prints: Clicked!
```
2024-09-22 14:19:12 +00:00
..
benches bevy_reflect: Add Function trait (#15205) 2024-09-22 14:19:12 +00:00
Cargo.toml Fix CI bench compile check (#14728) 2024-08-14 13:23:00 +00:00
README.md Add README to benches (#11508) 2024-01-24 17:11:28 +00:00

Bevy Benchmarks

This is a crate with a collection of benchmarks for Bevy, separate from the rest of the Bevy crates.

Running the benchmarks

  1. Setup everything you need for Bevy with the setup guide.

  2. Move into the benches directory (where this README is located).

    bevy $ cd benches
    
  3. Run the benchmarks with cargo (This will take a while)

    bevy/benches $ cargo bench
    

    If you'd like to only compile the benchmarks (without running them), you can do that like this:

    bevy/benches $ cargo bench --no-run
    

Criterion

Bevy's benchmarks use Criterion. If you want to learn more about using Criterion for comparing performance against a baseline or generating detailed reports, you can read the Criterion.rs documentation.