Struct CastTable

pub struct CastTable {
    table: HashMap<TypeId, Caster>,
}

A collection of functions to downcast &dyn Object references for some particular concrete object type O into various &dyn Trait references.

You shouldn’t construct this on your own: instead use derive_deftly(Object).

You shouldn’t use this directly; instead use ObjectArcExt.

Note that the concrete object type O is not represented in the type of CastTable; CastTables are obtained and used at runtime, as part of dynamic dispatch, so the type O is erased. We work with TypeIds and various &dyn ....

Fields

table: HashMap<TypeId, Caster>

A mapping from target TypeId for some trait to a function that can convert this table’s type into a trait pointer to that trait.

Every entry in this table must contain:

• A key that is typeid::of::<&'static dyn Tr>() for some trait Tr.
• A Caster whose functions are suitable for casting objects from this table’s type to dyn Tr.

Implementations

impl CastTable

pub fn insert<T: 'static + ?Sized>( &mut self, cast_to_ref: fn(_: &dyn Object) -> &T, cast_to_arc: fn(_: Arc<dyn Object>) -> Arc<T>, )

Add a new entry to this CastTable for downcasting to TypeId.

You should not call this yourself; instead use derive_deftly(Object)

Requirements

T must be dyn Tr for some trait Tr. (Not checked by the compiler.)

cast_to_ref is a downcaster from &dyn Object to &dyn Tr.

cast_to_arc is a downcaster from Arc<dyn Object> to Arc<dyn Tr>.

These functions SHOULD panic if the concrete type of its argument is not the concrete type O associated with this CastTable.

O must be 'static. (Checked by the compiler.)

Panics

Panics if called twice on the same CastTable with the same Tr.

fn insert_erased(&mut self, type_id: TypeId, caster: Caster)

Implementation for adding an entry to the CastTable

Broken out for clarity and to reduce monomorphisation.

Requirements

Like insert, but less compile-time checking. type_id is the identity of &'static dyn Tr, and func has been boxed and type-erased.

pub fn cast_object_to<'a, T: 'static + ?Sized>( &self, obj: &'a dyn Object, ) -> Option<&'a T>

Try to downcast a reference to an object whose concrete type is O (the type associated with this CastTable) to some target type T.

T should be dyn Tr. If T is not one of the dyn Tr for which insert was called, returns None.

Panics

Panics if the concrete type of obj does not match O.

May panic if any of the Requirements for CastTable::insert were violated.

pub fn cast_object_to_arc<T: 'static + ?Sized>( &self, obj: Arc<dyn Object>, ) -> Result<Arc<T>, Arc<dyn Object>>

As cast_object_to, but returns an Arc<dyn Tr>.

If T is not one of the dyn Tr types for which insert_arc was called, return Err(obj).

Panics

Panics if the concrete type of obj does not match O.

May panic if any of the Requirements for CastTable::insert were violated.

Trait Implementations

impl Default for CastTable

fn default() -> CastTable

Returns the “default value” for a type.