Trait Property 

pub trait Property<E: Entity>:
    Copy
    + Debug
    + PartialEq
    + 'static {
    type QueryParts<'a>: AsRef<[&'a dyn Any]>
       where Self: 'a;

    const NAME: &'static str;

    // Required methods
    fn initialization_kind() -> PropertyInitializationKind;
    fn compute_derived(context: &Context, entity_id: EntityId<E>) -> Self;
    fn default_const() -> Self;
    fn get_display(&self) -> String;
    fn query_parts_for_value(value: &Self) -> Self::QueryParts<'_>;
    fn id() -> usize;
    fn collect_non_derived_dependencies(result: &mut HashSet<usize>);

    // Provided methods
    fn name() -> &'static str { ... }
    fn is_derived() -> bool { ... }
    fn is_required() -> bool { ... }
    fn value_from_query_parts(parts: &[&dyn Any]) -> Option<Self> { ... }
    fn type_id() -> TypeId { ... }
    fn non_derived_dependencies() -> Vec<usize> { ... }
    fn dependents() -> &'static [usize] { ... }
}

All properties must implement this trait using one of the define_property macros.

Property values must be copyable and comparable for equality so storage and unindexed query scans can operate on them. Indexed properties must additionally implement IndexableProperty.

Required Associated Constants

const NAME: &'static str

Source-level name, set by the macros to stringify!($property).

Required Associated Types

type QueryParts<'a>: AsRef<[&'a dyn Any]> where Self: 'a

Allocation-free representation of the query parts contributed by a property value.

Required Methods

fn initialization_kind() -> PropertyInitializationKind

The kind of initialization this property has.

fn compute_derived(context: &Context, entity_id: EntityId<E>) -> Self

Compute the value of the property, possibly by accessing the context and using the entity’s ID.

fn default_const() -> Self

Return the default initial constant value.

fn get_display(&self) -> String

Returns a string representation of the property value, e.g. for writing to a CSV file.

fn query_parts_for_value(value: &Self) -> Self::QueryParts<'_>

Expose the query parts for a concrete property value without allocating.

Ordinary properties contribute a single value. Multi-properties override this so singleton queries over a multi-property can still be matched against the representative multi-property for the equivalent component set.

fn id() -> usize

For implementing the registry pattern

fn collect_non_derived_dependencies(result: &mut HashSet<usize>)

An auxiliary helper for non_derived_dependencies above.

Provided Methods

fn name() -> &'static str

fn is_derived() -> bool

fn is_required() -> bool

fn value_from_query_parts(parts: &[&dyn Any]) -> Option<Self>

Reconstruct the property value used for indexed lookup.

Ordinary properties expect a single query part containing Self. Multi-properties override this to rebuild their declared tuple value directly from already-sorted type-erased query parts.

fn type_id() -> TypeId

The logical type identity for this property.

fn non_derived_dependencies() -> Vec<usize>

Returns a vector of transitive non-derived dependencies. If the property is not derived, the Vec will be empty. The dependencies are represented by their Property<E>::id() value.

This function is only used to construct the static dependency graph within property ctors, after which time the dependents of a property are accessible through Property<E>::dependents() as a &'static [usize].

fn dependents() -> &'static [usize]

Get a list of derived properties that depend on this property. The properties are represented by their Property::id(). The list is pre-computed in ctors.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementors