# Objective
Closes#7622.
I was working on adding support for reflecting generic functions and
found that I wanted to use an argument's `TypeId` for hashing and
comparison, but its `TypePath` for debugging and error messaging.
While I could just keep them separate, place them in a tuple or a local
struct or something, I think I see an opportunity to make a dedicate
type for this.
Additionally, we can use this type to clean up some duplication amongst
the type info structs in a manner similar to #7622.
## Solution
Added the `Type` type. This should be seen as the most basic
representation of a type apart from `TypeId`. It stores both the
`TypeId` of the type as well as its `TypePathTable`.
The `Hash` and `PartialEq` implementations rely on the `TypeId`, while
the `Debug` implementation relies on the `TypePath`.
This makes it especially useful as a key in a `HashMap` since we get the
speed of the `TypeId` hashing/comparisons with the readability of
`TypePath`.
With this type, we're able to reduce the duplication across the type
info structs by removing individual fields for `TypeId` and
`TypePathTable`, replacing them with a single `Type` field. Similarly,
we can remove many duplicate methods and replace it with a macro that
delegates to the stored `Type`.
### Caveats
It should be noted that this type is currently 3x larger than `TypeId`.
On my machine, it's 48 bytes compared to `TypeId`'s 16. While this
doesn't matter for `TypeInfo` since it would contain that data
regardless, it is something to keep in mind when using elsewhere.
## Testing
All tests should pass as normal:
```
cargo test --package bevy_reflect
```
---
## Showcase
`bevy_reflect` now exports a `Type` struct. This type contains both the
`TypeId` and the `TypePathTable` of the given type, allowing it to be
used like `TypeId` but have the debuggability of `TypePath`.
```rust
// We can create this for any type implementing `TypePath`:
let ty = Type::of::<String>();
// It has `Hash` and `Eq` impls powered by `TypeId`, making it useful for maps:
let mut map = HashMap::<Type, i32>::new();
map.insert(ty, 25);
// And it has a human-readable `Debug` representation:
let debug = format!("{:?}", map);
assert_eq!(debug, "{alloc::string::String: 25}");
```
## Migration Guide
Certain type info structs now only return their item types as `Type`
instead of exposing direct methods on them.
The following methods have been removed:
- `ArrayInfo::item_type_path_table`
- `ArrayInfo::item_type_id`
- `ArrayInfo::item_is`
- `ListInfo::item_type_path_table`
- `ListInfo::item_type_id`
- `ListInfo::item_is`
- `SetInfo::value_type_path_table`
- `SetInfo::value_type_id`
- `SetInfo::value_is`
- `MapInfo::key_type_path_table`
- `MapInfo::key_type_id`
- `MapInfo::key_is`
- `MapInfo::value_type_path_table`
- `MapInfo::value_type_id`
- `MapInfo::value_is`
Instead, access the `Type` directly using one of the new methods:
- `ArrayInfo::item_ty`
- `ListInfo::item_ty`
- `SetInfo::value_ty`
- `MapInfo::key_ty`
- `MapInfo::value_ty`
For example:
```rust
// BEFORE
let type_id = array_info.item_type_id();
// AFTER
let type_id = array_info.item_ty().id();
```
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