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// From 'Learning Rust' "dyn PartialEq"

use std::any::Any;

pub trait AsDynCompare: Any {
    fn as_any(&self) -> &dyn Any;
    fn as_dyn_compare(&self) -> &dyn DynCompare;
}

impl<T: Any + DynCompare> AsDynCompare for T {
    fn as_any(&self) -> &dyn Any {
        self
    }
    fn as_dyn_compare(&self) -> &dyn DynCompare {
        self
    }
}

pub trait DynCompare: AsDynCompare {
    fn dyn_eq(&self, other: &dyn DynCompare) -> bool;
}

impl<T: Any + PartialEq> DynCompare for T {
    fn dyn_eq(&self, other: &dyn DynCompare) -> bool {
        if let Some(other) = other.as_any().downcast_ref::<Self>() {
            self == other
        } else {
            false
        }
    }
}

// n.b. this could be implemented in a more general way when
// the trait object lifetime is not constrained to `'static`
impl PartialEq<dyn DynCompare> for dyn DynCompare {
    fn eq(&self, other: &dyn DynCompare) -> bool {
        self.dyn_eq(other)
    }
}