Attribute Macro cast_trait_object::dyn_cast

#[dyn_cast]

This is supported on crate feature proc-macros only.

Allow attempting to cast a trait object to another trait object. This can be used on traits or on types. For types you need to specify the path to the "source" trait inside the parenthesis after the macro name like so: #[dyn_cast(SourceTrait => TargetTrait)], while for traits you only need to specify the target trait: #[dyn_cast(TargetTrait)].

Examples

use cast_trait_object::*;

#[dyn_cast(Sub)]
trait Super {}

trait Sub: Super {}

#[dyn_cast(Super => Sub)]
struct Foo;
impl Super for Foo {}
impl Sub for Foo {}

// We can now attempt casting between trait objects:
let foo: &dyn Super = &Foo;
let foo: &dyn Sub = foo.dyn_cast().ok().unwrap();

The macro can also be applied to a trait implementation (impl Trait for Type) instead of directly on a type:

#[dyn_cast(Sub)]
impl Super for Foo {}