Phaiax · June 20, 2017 13:15 · Jun 20, 2017
diff --git a/error_chain_extension.rs b/error_chain_extension.rs
@@ -0,0 +1,106 @@
+#[macro_use] extern crate error_chain;
+
+
+// All errors that can occour everywhere in the crate
+pub mod errors {
+    error_chain!{
+        errors {
+            Pig { description("Pig-Descr") display("Pig-Display")}
+            Bat {}
+            Uhu {}
+        }
+    }
+}
+
+pub use errors::*;
+
+
+
+// Every public fn is preceeded by this macro which indicates the valid
+// variants of errors that can occour.
+// can_err!( AErrorKinds, AResult, {Pig, Bat})
+////////////////////////////////////////////////////////
+////////// THIS WOULD BE GENERATED BY THE MACRO can_err!
+////////////////////////////////////////////////////////
+#[derive(Debug)]
+pub enum AErrorKinds {
+    Pig{k : Error},
+    Bat{k : Error}
+}
+pub type AResult<T> = std::result::Result<T, AErrorKinds>;
+impl AErrorKinds {
+    pub fn kind(&self) -> &ErrorKind {
+        match self {
+            &AErrorKinds::Pig { ref k } => k.kind(),
+            &AErrorKinds::Bat { ref k } => k.kind(),
+        }
+    }
+    pub fn kind_reduced(&self) -> &AErrorKinds {
+        self
+    }
+    pub fn description(&self) -> &str {
+        self.kind().description()
+    }
+}
+impl std::fmt::Display for AErrorKinds {
+    fn fmt(&self, fmt: &mut std::fmt::Formatter) -> std::fmt::Result {
+        //use std::fmt::Display;
+        self.kind().fmt(fmt)
+    }
+}
+impl From<ErrorKind> for AErrorKinds {
+    fn from(ek: ErrorKind) -> Self {
+        let e : Error = ek.into();
+        let n = match e.kind() {
+            &ErrorKind::Pig{..} => 1,
+            &ErrorKind::Bat{..} => 2,
+            _ => unreachable!()
+        };
+        match n {
+            1 => AErrorKinds::Pig { k:e },
+            2 => AErrorKinds::Bat { k:e },
+            _ => unreachable!()
+        }
+    }
+}
+////////////////////////////////////////////////////////
+///////////////////   END MACRO
+////////////////////////////////////////////////////////
+
+fn some_internal_helper() -> AResult<u8> {
+    // Uhu is an invalid error for this
+    // function, so the following line will go to unreachable! and panic.
+    Err(ErrorKind::Uhu.into())
+}
+
+
+
+#[cfg(test)]
+mod tests {
+
+    use super::*;
+
+    #[test]
+    fn it_works() {
+
+        if let Err(err) = some_internal_helper() {
+            match *err.kind() {
+                ErrorKind::Msg(_) => {}
+                ErrorKind::Pig => {},
+                ErrorKind::Bat => {}
+                ErrorKind::Uhu => {}
+            }
+            // the actual errors that can be generated by the function
+            // are combined in a distict enum that allows exhaustive
+            // matching
+            match *err.kind_reduced() {
+                AErrorKinds::Pig{..} => {},
+                AErrorKinds::Bat{..} => {}
+            }
+            println!("Descr: {}", err.description());
+            println!("Displ: {}", err);
+            println!("Debug: {:?}", err);
+        }
+
+    }
+}