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//! Shows how to implement `MapAs` to allow type-erased access to a mapped
//! type.
//!
//! Because ["custom DSTs are a largely half-baked feature for
//! now"][rustnomicon], this crate cannot directly wrap dynamically sized types
//! such as dynamic trait objects due to how its data structures work and the
//! required features being unstable.
//!
//! The `MapAs` trait allows a DST to be used as the `MapAs::Target` type,
//! and this enables `AnyRef` to load a reference to the `MapAs::Target` type
//! of any stored type.
//!
//! [rustnomicon]:
//!     https://doc.rust-lang.org/nomicon/exotic-sizes.html#dynamically-sized-types-dsts

use refuse::{AnyRef, CollectionGuard, MapAs, Ref, Trace};

trait SomeTrait {
    fn do_something(&self);
}

#[derive(MapAs, Trace)]
#[map_as(target = dyn SomeTrait)]
struct SomeType;

impl SomeTrait for SomeType {
    fn do_something(&self) {
        println!("Did something!");
    }
}

fn main() {
    let guard = CollectionGuard::acquire();
    let gced: Ref<SomeType> = Ref::new(SomeType, &guard);
    let type_erased: AnyRef = gced.as_any();
    type_erased
        .load_mapped::<dyn SomeTrait>(&guard)
        .unwrap()
        .do_something();
}