1 files changed, 273 insertions, 0 deletions
diff --git a/src/private/cast/mod.rs b/src/private/cast/mod.rs
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+//! Originally from Intertrait by CodeChain
+//!
+//! <https://github.com/CodeChain-io/intertrait>
+//! <https://crates.io/crates/intertrait/0.2.2>
+//!
+//! Licensed under either of
+//!
+//! Apache License, Version 2.0 (LICENSE-APACHE or <http://www.apache.org/licenses/LICENSE-2.0>)
+//! MIT license (LICENSE-MIT or <http://opensource.org/licenses/MIT>)
+//!
+//! at your option.
+use std::any::{Any, TypeId};
+use std::rc::Rc;
+use std::sync::Arc;
+
+use ahash::AHashMap;
+use linkme::distributed_slice;
+use once_cell::sync::Lazy;
+
+pub mod arc;
+pub mod boxed;
+pub mod error;
+pub mod rc;
+
+pub type BoxedCaster = Box<dyn Any + Send + Sync>;
+
+/// A distributed slice gathering constructor functions for [`Caster`]s.
+///
+/// A constructor function returns `TypeId` of a concrete type involved in the casting
+/// and a `Box` of a type or trait backed by a [`Caster`].
+#[distributed_slice]
+pub static CASTERS: [fn() -> (TypeId, BoxedCaster)] = [..];
+
+/// A `HashMap` mapping `TypeId` of a [`Caster`] to an instance of it.
+static CASTER_MAP: Lazy<AHashMap<(TypeId, TypeId), BoxedCaster>> = Lazy::new(|| {
+    CASTERS
+        .iter()
+        .map(|caster_fn| {
+            let (type_id, caster) = caster_fn();
+
+            ((type_id, (*caster).type_id()), caster)
+        })
+        .collect()
+});
+
+type CastBoxFn<Dest> = fn(from: Box<dyn Any>) -> Result<Box<Dest>, CasterError>;
+
+type CastRcFn<Dest> = fn(from: Rc<dyn Any>) -> Result<Rc<Dest>, CasterError>;
+
+type CastArcFn<Dest> =
+    fn(from: Arc<dyn Any + Sync + Send + 'static>) -> Result<Arc<Dest>, CasterError>;
+
+/// A `Caster` knows how to cast a type or trait to the type or trait `Dest`. Each
+/// `Caster` instance is specific to a concrete type. That is, it knows how to cast to
+/// single specific type or trait implemented by single specific type.
+pub struct Caster<Dest: ?Sized + 'static>
+{
+    /// Casts a `Box` holding a type or trait object for `Any` to another `Box` holding a
+    /// type or trait `Dest`.
+    pub cast_box: CastBoxFn<Dest>,
+
+    /// Casts an `Rc` holding a type or trait for `Any` to another `Rc` holding a type or
+    /// trait `Dest`.
+    pub cast_rc: CastRcFn<Dest>,
+
+    /// Casts an `Arc` holding a type or trait for `Any + Sync + Send + 'static` to
+    /// another `Arc` holding a type or trait for `Dest`.
+    pub opt_cast_arc: Option<CastArcFn<Dest>>,
+}
+
+impl<Dest: ?Sized + 'static> Caster<Dest>
+{
+    pub fn new(cast_box: CastBoxFn<Dest>, cast_rc: CastRcFn<Dest>) -> Caster<Dest>
+    {
+        Caster::<Dest> {
+            cast_box,
+            cast_rc,
+            opt_cast_arc: None,
+        }
+    }
+
+    #[allow(clippy::similar_names)]
+    pub fn new_sync(
+        cast_box: CastBoxFn<Dest>,
+        cast_rc: CastRcFn<Dest>,
+        cast_arc: CastArcFn<Dest>,
+    ) -> Caster<Dest>
+    {
+        Caster::<Dest> {
+            cast_box,
+            cast_rc,
+            opt_cast_arc: Some(cast_arc),
+        }
+    }
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum CasterError
+{
+    #[error("Failed to cast Box")]
+    CastBoxFailed,
+
+    #[error("Failed to cast Rc")]
+    CastRcFailed,
+
+    #[error("Failed to cast Arc")]
+    CastArcFailed,
+}
+
+/// Returns a `Caster<Dest>` from a concrete type with the id `type_id` to a type or trait
+/// `Dest`.
+fn get_caster<Dest: ?Sized + 'static>(
+    type_id: TypeId,
+) -> Result<&'static Caster<Dest>, GetCasterError>
+{
+    let any_caster = CASTER_MAP
+        .get(&(type_id, TypeId::of::<Caster<Dest>>()))
+        .ok_or(GetCasterError::NotFound)?;
+
+    any_caster
+        .downcast_ref::<Caster<Dest>>()
+        .ok_or(GetCasterError::DowncastFailed)
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum GetCasterError
+{
+    #[error("Caster not found")]
+    NotFound,
+
+    #[error("Failed to downcast caster")]
+    DowncastFailed,
+}
+
+/// `CastFrom` must be extended by a trait that wants to allow for casting into another
+/// trait.
+///
+/// It is used for obtaining a trait object for [`Any`] from a trait object for its
+/// sub-trait, and blanket implemented for all `Sized + Any + 'static` types.
+///
+/// # Examples
+/// ```ignore
+/// trait Source: CastFrom {
+///     ...
+/// }
+/// ```
+pub trait CastFrom: Any + 'static
+{
+    /// Returns a `Box` of `Any`, which is backed by the type implementing this trait.
+    fn box_any(self: Box<Self>) -> Box<dyn Any>;
+
+    /// Returns an `Rc` of `Any`, which is backed by the type implementing this trait.
+    fn rc_any(self: Rc<Self>) -> Rc<dyn Any>;
+}
+
+/// `CastFromSync` must be extended by a trait that is `Any + Sync + Send + 'static`
+/// and wants to allow for casting into another trait behind references and smart pointers
+/// especially including `Arc`.
+///
+/// It is used for obtaining a trait object for [`Any + Sync + Send + 'static`] from an
+/// object for its sub-trait, and blanket implemented for all `Sized + Sync + Send +
+/// 'static` types.
+///
+/// # Examples
+/// ```ignore
+/// trait Source: CastFromSync {
+///     ...
+/// }
+/// ```
+pub trait CastFromSync: CastFrom + Sync + Send + 'static
+{
+    fn arc_any(self: Arc<Self>) -> Arc<dyn Any + Sync + Send + 'static>;
+}
+
+impl<Source: Sized + Any + 'static> CastFrom for Source
+{
+    fn box_any(self: Box<Self>) -> Box<dyn Any>
+    {
+        self
+    }
+
+    fn rc_any(self: Rc<Self>) -> Rc<dyn Any>
+    {
+        self
+    }
+}
+
+impl CastFrom for dyn Any + 'static
+{
+    fn box_any(self: Box<Self>) -> Box<dyn Any>
+    {
+        self
+    }
+
+    fn rc_any(self: Rc<Self>) -> Rc<dyn Any>
+    {
+        self
+    }
+}
+
+impl<Source: Sized + Sync + Send + 'static> CastFromSync for Source
+{
+    fn arc_any(self: Arc<Self>) -> Arc<dyn Any + Sync + Send + 'static>
+    {
+        self
+    }
+}
+
+impl CastFrom for dyn Any + Sync + Send + 'static
+{
+    fn box_any(self: Box<Self>) -> Box<dyn Any>
+    {
+        self
+    }
+
+    fn rc_any(self: Rc<Self>) -> Rc<dyn Any>
+    {
+        self
+    }
+}
+
+impl CastFromSync for dyn Any + Sync + Send + 'static
+{
+    fn arc_any(self: Arc<Self>) -> Arc<dyn Any + Sync + Send + 'static>
+    {
+        self
+    }
+}
+
+#[cfg(test)]
+mod tests
+{
+    use std::any::TypeId;
+    use std::fmt::Debug;
+
+    use linkme::distributed_slice;
+
+    use super::*;
+    use crate::test_utils::subjects;
+
+    #[distributed_slice(super::CASTERS)]
+    static TEST_CASTER: fn() -> (TypeId, BoxedCaster) = create_test_caster;
+
+    fn create_test_caster() -> (TypeId, BoxedCaster)
+    {
+        let type_id = TypeId::of::<subjects::Ninja>();
+
+        let caster = Box::new(Caster::<dyn Debug> {
+            cast_box: |from| {
+                let concrete = from
+                    .downcast::<subjects::Ninja>()
+                    .map_err(|_| CasterError::CastBoxFailed)?;
+
+                Ok(concrete as Box<dyn Debug>)
+            },
+            cast_rc: |from| {
+                let concrete = from
+                    .downcast::<subjects::Ninja>()
+                    .map_err(|_| CasterError::CastRcFailed)?;
+
+                Ok(concrete as Rc<dyn Debug>)
+            },
+            opt_cast_arc: Some(|from| {
+                let concrete = from
+                    .downcast::<subjects::Ninja>()
+                    .map_err(|_| CasterError::CastArcFailed)?;
+
+                Ok(concrete as Arc<dyn Debug>)
+            }),
+        });
+        (type_id, caster)
+    }
+}