1df8238e8d
# Objective
The `NestedLoader` API as it stands right now is somewhat lacking:
- It consists of several types `NestedLoader`, `UntypedNestedLoader`,
`DirectNestedLoader`, and `UntypedDirectNestedLoader`, where a typestate
pattern on `NestedLoader` would be make it more obvious what it does,
and allow centralising the documentation
- The term "untyped" in the asset loader code is overloaded. It can mean
either:
- we have literally no idea what the type of this asset will be when we
load it (I dub this "unknown type")
- we know what type of asset it will be, but we don't know it statically
- we only have a TypeId (I dub this "dynamic type" / "erased")
- There is no way to get an `UntypedHandle` (erased) given a `TypeId`
## Solution
Changes `NestedLoader` into a type-state pattern, adding two type
params:
- `T` determines the typing
- `StaticTyped`, the default, where you pass in `A` statically into `fn
load<A>() -> ..`
- `DynamicTyped`, where you give a `TypeId`, giving you a
`UntypedHandle`
- `UnknownTyped`, where you have literally no idea what type of asset
you're loading, giving you a `Handle<LoadedUntypedAsset>`
- `M` determines the "mode" (bikeshedding TBD, I couldn't come up with a
better name)
- `Deferred`, the default, won't load the asset when you call `load`,
but it does give you a `Handle` to it (this is nice since it can be a
sync fn)
- `Immediate` will load the asset as soon as you call it, and give you
access to it, but you must be in an async context to call it
Changes some naming of internals in `AssetServer` to fit the new
definitions of "dynamic type" and "unknown type". Note that I didn't do
a full pass over this code to keep the diff small. That can probably be
done in a new PR - I think the definiton I laid out of unknown type vs.
erased makes it pretty clear where each one applies.
<details>
<summary>Old issue</summary>
The only real problem I have with this PR is the requirement to pass in
`type_name` (from `core::any::type_name`) into Erased. Users might not
have that type name, only the ID, and it just seems sort of weird to
*have* to give an asset type name. However, the reason we need it is
because of this:
```rs
pub(crate) fn get_or_create_path_handle_erased(
&mut self,
path: AssetPath<'static>,
type_id: TypeId,
type_name: &str,
loading_mode: HandleLoadingMode,
meta_transform: Option<MetaTransform>,
) -> (UntypedHandle, bool) {
let result = self.get_or_create_path_handle_internal(
path,
Some(type_id),
loading_mode,
meta_transform,
);
// it is ok to unwrap because TypeId was specified above
unwrap_with_context(result, type_name).unwrap()
}
pub(crate) fn unwrap_with_context<T>(
result: Result<T, GetOrCreateHandleInternalError>,
type_name: &str,
) -> Option<T> {
match result {
Ok(value) => Some(value),
Err(GetOrCreateHandleInternalError::HandleMissingButTypeIdNotSpecified) => None,
Err(GetOrCreateHandleInternalError::MissingHandleProviderError(_)) => {
panic!("Cannot allocate an Asset Handle of type '{type_name}' because the asset type has not been initialized. \
Make sure you have called app.init_asset::<{type_name}>()")
}
}
}
```
This `unwrap_with_context` is literally the only reason we need the
`type_name`. Potentially, this can be turned into an `impl
Into<Option<&str>>`, and output a different error message if the type
name is missing. Since if we are loading an asset where we only know the
type ID, by definition we can't output that error message, since we
don't have the type name. I'm open to suggestions on this.
</details>
## Testing
Not sure how to test this, since I kept most of the actual NestedLoader
logic the same. The only new API is loading an `UntypedHandle` when in
the `DynamicTyped, Immediate` state.
## Migration Guide
Code which uses `bevy_asset`'s `LoadContext::loader` / `NestedLoader`
will see some naming changes:
- `untyped` is replaced by `with_unknown_type`
- `with_asset_type` is replaced by `with_static_type`
- `with_asset_type_id` is replaced by `with_dynamic_type`
- `direct` is replaced by `immediate` (the opposite of "immediate" is
"deferred")
|
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|---|---|---|
| .cargo | ||
| .github | ||
| assets | ||
| benches | ||
| crates | ||
| docs | ||
| docs-template | ||
| errors | ||
| examples | ||
| src | ||
| tests | ||
| tools | ||
| .gitattributes | ||
| .gitignore | ||
| Cargo.toml | ||
| clippy.toml | ||
| CODE_OF_CONDUCT.md | ||
| CONTRIBUTING.md | ||
| CREDITS.md | ||
| deny.toml | ||
| LICENSE-APACHE | ||
| LICENSE-MIT | ||
| README.md | ||
| rustfmt.toml | ||
| typos.toml | ||
What is Bevy?
Bevy is a refreshingly simple data-driven game engine built in Rust. It is free and open-source forever!
WARNING
Bevy is still in the early stages of development. Important features are missing. Documentation is sparse. A new version of Bevy containing breaking changes to the API is released approximately once every 3 months. We provide migration guides, but we can't guarantee migrations will always be easy. Use only if you are willing to work in this environment.
MSRV: Bevy relies heavily on improvements in the Rust language and compiler. As a result, the Minimum Supported Rust Version (MSRV) is generally close to "the latest stable release" of Rust.
Design Goals
- Capable: Offer a complete 2D and 3D feature set
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Follow the Setup guide to ensure your development environment is set up correctly. Once set up, you can quickly try out the examples by cloning this repo and running the following commands:
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fn main(){
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}
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