5 files changed, 75 insertions, 18 deletions
diff --git a/src/libs/intertrait/cast/arc.rs b/src/libs/intertrait/cast/arc.rs
index 4099ae7..f8e0f11 100644
--- a/src/libs/intertrait/cast/arc.rs
+++ b/src/libs/intertrait/cast/arc.rs
@@ -9,24 +9,36 @@
 //! MIT license (LICENSE-MIT or <http://opensource.org/licenses/MIT>)
 //!
 //! at your option.
+use std::any::type_name;
 use std::sync::Arc;
 
+use error_stack::report;
+
+use crate::libs::intertrait::cast::error::CastError;
 use crate::libs::intertrait::{caster, CastFromSync};
 
 pub trait CastArc
 {
-    /// Casts an `Arc` for this trait into that for type `T`.
-    fn cast<T: ?Sized + 'static>(self: Arc<Self>) -> Result<Arc<T>, Arc<Self>>;
+    /// Casts an `Arc` for this trait into that for type `OtherTrait`.
+    fn cast<OtherTrait: ?Sized + 'static>(
+        self: Arc<Self>,
+    ) -> error_stack::Result<Arc<OtherTrait>, CastError>;
 }
 
 /// A blanket implementation of `CastArc` for traits extending `CastFrom`, `Sync`, and `Send`.
-impl<S: ?Sized + CastFromSync> CastArc for S
+impl<CastFromSelf: ?Sized + CastFromSync> CastArc for CastFromSelf
 {
-    fn cast<T: ?Sized + 'static>(self: Arc<Self>) -> Result<Arc<T>, Arc<Self>>
+    fn cast<OtherTrait: ?Sized + 'static>(
+        self: Arc<Self>,
+    ) -> error_stack::Result<Arc<OtherTrait>, CastError>
     {
-        match caster::<T>((*self).type_id()) {
+        match caster::<OtherTrait>((*self).type_id()) {
             Some(caster) => Ok((caster.cast_arc)(self.arc_any())),
-            None => Err(self),
+            None => Err(report!(CastError).attach_printable(format!(
+                "From {} to {}",
+                type_name::<CastFromSelf>(),
+                type_name::<OtherTrait>()
+            ))),
         }
     }
 }
diff --git a/src/libs/intertrait/cast/box.rs b/src/libs/intertrait/cast/box.rs
index c88fb84..11f631a 100644
--- a/src/libs/intertrait/cast/box.rs
+++ b/src/libs/intertrait/cast/box.rs
@@ -9,22 +9,36 @@
 //! MIT license (LICENSE-MIT or <http://opensource.org/licenses/MIT>)
 //!
 //! at your option.
+
+use std::any::type_name;
+
+use error_stack::report;
+
+use crate::libs::intertrait::cast::error::CastError;
 use crate::libs::intertrait::{caster, CastFrom};
 
 pub trait CastBox
 {
-    /// Casts a box to this trait into that of type `T`. If fails, returns the receiver.
-    fn cast<T: ?Sized + 'static>(self: Box<Self>) -> Result<Box<T>, Box<Self>>;
+    /// Casts a box to this trait into that of type `OtherTrait`.
+    fn cast<OtherTrait: ?Sized + 'static>(
+        self: Box<Self>,
+    ) -> error_stack::Result<Box<OtherTrait>, CastError>;
 }
 
 /// A blanket implementation of `CastBox` for traits extending `CastFrom`.
-impl<S: ?Sized + CastFrom> CastBox for S
+impl<CastFromSelf: ?Sized + CastFrom> CastBox for CastFromSelf
 {
-    fn cast<T: ?Sized + 'static>(self: Box<Self>) -> Result<Box<T>, Box<Self>>
+    fn cast<OtherTrait: ?Sized + 'static>(
+        self: Box<Self>,
+    ) -> error_stack::Result<Box<OtherTrait>, CastError>
     {
-        match caster::<T>((*self).type_id()) {
+        match caster::<OtherTrait>((*self).type_id()) {
             Some(caster) => Ok((caster.cast_box)(self.box_any())),
-            None => Err(self),
+            None => Err(report!(CastError).attach_printable(format!(
+                "From {} to {}",
+                type_name::<CastFromSelf>(),
+                type_name::<OtherTrait>()
+            ))),
         }
     }
 }
diff --git a/src/libs/intertrait/cast/error.rs b/src/libs/intertrait/cast/error.rs
new file mode 100644
index 0000000..e4211b1
--- /dev/null
+++ b/src/libs/intertrait/cast/error.rs
@@ -0,0 +1,17 @@
+use std::fmt;
+use std::fmt::{Display, Formatter};
+
+use error_stack::Context;
+
+#[derive(Debug)]
+pub struct CastError;
+
+impl Display for CastError
+{
+    fn fmt(&self, fmt: &mut Formatter<'_>) -> fmt::Result
+    {
+        fmt.write_str("Failed to cast between traits")
+    }
+}
+
+impl Context for CastError {}
diff --git a/src/libs/intertrait/cast/mod.rs b/src/libs/intertrait/cast/mod.rs
index 83f7210..a0342cf 100644
--- a/src/libs/intertrait/cast/mod.rs
+++ b/src/libs/intertrait/cast/mod.rs
@@ -9,6 +9,8 @@
 //! MIT license (LICENSE-MIT or <http://opensource.org/licenses/MIT>)
 //!
 //! at your option.
+pub mod error;
+
 mod arc;
 mod r#box;
 mod rc;
diff --git a/src/libs/intertrait/cast/rc.rs b/src/libs/intertrait/cast/rc.rs
index b53ced0..6cd377e 100644
--- a/src/libs/intertrait/cast/rc.rs
+++ b/src/libs/intertrait/cast/rc.rs
@@ -9,24 +9,36 @@
 //! MIT license (LICENSE-MIT or <http://opensource.org/licenses/MIT>)
 //!
 //! at your option.
+use std::any::type_name;
 use std::rc::Rc;
 
+use error_stack::report;
+
+use crate::libs::intertrait::cast::error::CastError;
 use crate::libs::intertrait::{caster, CastFrom};
 
 pub trait CastRc
 {
-    /// Casts an `Rc` for this trait into that for type `T`.
-    fn cast<T: ?Sized + 'static>(self: Rc<Self>) -> Result<Rc<T>, Rc<Self>>;
+    /// Casts an `Rc` for this trait into that for type `OtherTrait`.
+    fn cast<OtherTrait: ?Sized + 'static>(
+        self: Rc<Self>,
+    ) -> error_stack::Result<Rc<OtherTrait>, CastError>;
 }
 
 /// A blanket implementation of `CastRc` for traits extending `CastFrom`.
-impl<S: ?Sized + CastFrom> CastRc for S
+impl<CastFromSelf: ?Sized + CastFrom> CastRc for CastFromSelf
 {
-    fn cast<T: ?Sized + 'static>(self: Rc<Self>) -> Result<Rc<T>, Rc<Self>>
+    fn cast<OtherTrait: ?Sized + 'static>(
+        self: Rc<Self>,
+    ) -> error_stack::Result<Rc<OtherTrait>, CastError>
     {
-        match caster::<T>((*self).type_id()) {
+        match caster::<OtherTrait>((*self).type_id()) {
             Some(caster) => Ok((caster.cast_rc)(self.rc_any())),
-            None => Err(self),
+            None => Err(report!(CastError).attach_printable(format!(
+                "From {} to {}",
+                type_name::<CastFromSelf>(),
+                type_name::<OtherTrait>()
+            ))),
         }
     }
 }