pub trait TypePath: 'static {
// Required methods
fn type_path() -> &'static str;
fn short_type_path() -> &'static str;
// Provided methods
fn type_ident() -> Option<&'static str> { ... }
fn crate_name() -> Option<&'static str> { ... }
fn module_path() -> Option<&'static str> { ... }
}Expand description
A static accessor to type paths and names.
The engine uses this trait over std::any::type_name for stability and flexibility.
This trait is automatically implemented by the #[derive(Reflect)] macro
and allows type path information to be processed without an instance of that type.
Implementors may have difficulty in generating references with static lifetimes. Luckily, this crate comes with some utility structs, to make generating these statics much simpler.
Stability
Certain parts of the engine, e.g. (de)serialization, rely on type paths as identifiers for matching dynamic values to concrete types.
Using std::any::type_name, a scene containing my_crate::foo::MyComponent would break,
failing to deserialize if the component was moved from the foo module to the bar module,
becoming my_crate::bar::MyComponent.
This trait, through attributes when deriving itself or Reflect, can ensure breaking changes are avoidable.
The only external factor we rely on for stability when deriving is the module_path! macro,
only if the derive does not provide a #[type_path = "..."] attribute.
Anonymity
Some methods on this trait return Option<&'static str> over &'static str
because not all types define all parts of a type path, for example the array type [T; N].
Such types are ‘anonymous’ in that they have only a defined type_path and short_type_path
and the methods crate_name, module_path and type_ident all return None.
Primitives are treated like anonymous types, except they also have a defined type_ident.
Example
use bevy_reflect::TypePath;
// This type path will not change with compiler versions or recompiles,
// although it will not be the same if the definition is moved.
#[derive(TypePath)]
struct NonStableTypePath;
// This type path will never change, even if the definition is moved.
#[derive(TypePath)]
#[type_path = "my_crate::foo"]
struct StableTypePath;
// Type paths can have any number of path segments.
#[derive(TypePath)]
#[type_path = "my_crate::foo::bar::baz"]
struct DeeplyNestedStableTypePath;
// Including just a crate name!
#[derive(TypePath)]
#[type_path = "my_crate"]
struct ShallowStableTypePath;
// We can also rename the identifier/name of types.
#[derive(TypePath)]
#[type_path = "my_crate::foo"]
#[type_name = "RenamedStableTypePath"]
struct NamedStableTypePath;
// Generics are also supported.
#[derive(TypePath)]
#[type_path = "my_crate::foo"]
struct StableGenericTypePath<T, const N: usize>([T; N]);Required Methods§
fn type_path() -> &'static str
fn type_path() -> &'static str
Returns the fully qualified path of the underlying type.
Generic parameter types are also fully expanded.
For Option<PhantomData>, this is "core::option::Option<core::marker::PhantomData>".
fn short_type_path() -> &'static str
fn short_type_path() -> &'static str
Returns a short, pretty-print enabled path to the type.
Generic parameter types are also shortened.
For Option<PhantomData>, this is "Option<PhantomData>".