bevy_reflect: Add FunctionRegistry::call (#15148)

# Objective

There may be times where a function in the `FunctionRegistry` doesn't
need to be fully retrieved. A user may just need to call it with a set
of arguments.

We should provide a shortcut for doing this.

## Solution

Add the `FunctionRegistry::call` method to directly call a function in
the registry with the given name and arguments.

## Testing

You can test locally by running:

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

crates/bevy_reflect/src/func/registry.rs

@@ -4,7 +4,9 @@ use std::sync::{Arc, PoisonError, RwLock, RwLockReadGuard, RwLockWriteGuard};
 
 use bevy_utils::HashMap;
 
-use crate::func::{DynamicFunction, FunctionRegistrationError, IntoFunction};
+use crate::func::{
+ ArgList, DynamicFunction, FunctionRegistrationError, FunctionResult, IntoFunction,
+};
 
 /// A registry of [reflected functions].
 ///
@@ -282,6 +284,18 @@ impl FunctionRegistry {
  }
  }
 
+ /// Calls the function with the given [name] and [args].
+ ///
+ /// Returns `None` if no function with the given name is registered.
+ /// Otherwise, returns the result of the function call.
+ ///
+ /// [name]: DynamicFunction::name
+ /// [args]: ArgList
+ pub fn call<'a>(&self, name: &str, args: ArgList<'a>) -> Option<FunctionResult<'a>> {
+ let func = self.get(name)?;
+ Some(func.call(args))
+ }
+
  /// Get a reference to a registered function by [name].
  ///
  /// [name]: DynamicFunction::name
@@ -463,6 +477,23 @@ mod tests {
  assert_eq!(value.try_downcast_ref::<i32>(), Some(&321));
  }
 
+ #[test]
+ fn should_call_function_via_registry() {
+ fn add(a: i32, b: i32) -> i32 {
+ a + b
+ }
+
+ let mut registry = FunctionRegistry::default();
+ registry.register(add).unwrap();
+
+ let args = ArgList::new().push_owned(25_i32).push_owned(75_i32);
+ let result = registry
+ .call(std::any::type_name_of_val(&add), args)
+ .unwrap();
+ let value = result.unwrap().unwrap_owned();
+ assert_eq!(value.try_downcast_ref::<i32>(), Some(&100));
+ }
+
  #[test]
  fn should_error_on_missing_name() {
  let foo = || -> i32 { 123 };