Added VerificationError to replace formatted Strings

src/message/mod.rs

@@ -34,7 +34,7 @@ mod platform;
 mod platform;
 
 use self::platform::{send_unverified, send_super_unverified};
-use self::verify::verify_message_signature;
+use self::verify::{VerificationError, verify_message_signature};
 
 /// Specifies the superclass of an instance.
 #[repr(C)]
@@ -100,6 +100,7 @@ pub unsafe trait Message {
             where Self: Sized, A: EncodeArguments, R: Encode {
         let obj = unsafe { &*(self as *const _ as *const Object) };
         verify_message_signature::<A, R>(obj.class(), sel)
+            .map_err(MessageError::from)
     }
 }
 
@@ -169,6 +170,12 @@ impl Error for MessageError {
     }
 }
 
+impl<'a> From<VerificationError<'a>> for MessageError {
+    fn from(err: VerificationError) -> MessageError {
+        MessageError(err.to_string())
+    }
+}
+
 #[doc(hidden)]
 #[inline(always)]
 #[cfg(not(feature = "verify_message"))]
@@ -186,14 +193,13 @@ pub unsafe fn send_message<T, A, R>(obj: *const T, sel: Sel, args: A)
         where T: Message, A: MessageArguments + EncodeArguments,
         R: Any + Encode {
     let cls = if obj.is_null() {
-        return Err(MessageError(format!("Messaging {:?} to nil", sel)));
+        return Err(VerificationError::NilReceiver(sel).into());
     } else {
         (*(obj as *const Object)).class()
     };
 
-    verify_message_signature::<A, R>(cls, sel).and_then(|_| {
-        send_unverified(obj, sel, args)
-    })
+    verify_message_signature::<A, R>(cls, sel)?;
+    send_unverified(obj, sel, args)
 }
 
 #[doc(hidden)]
@@ -213,12 +219,11 @@ pub unsafe fn send_super_message<T, A, R>(obj: *const T, superclass: &Class,
         where T: Message, A: MessageArguments + EncodeArguments,
         R: Any + Encode {
     if obj.is_null() {
-        return Err(MessageError(format!("Messaging {:?} to nil", sel)));
+        return Err(VerificationError::NilReceiver(sel).into());
     }
 
-    verify_message_signature::<A, R>(superclass, sel).and_then(|_| {
-        send_super_unverified(obj, superclass, sel, args)
-    })
+    verify_message_signature::<A, R>(superclass, sel)?;
+    send_super_unverified(obj, superclass, sel, args)
 }
 
 #[cfg(test)]

src/message/verify.rs

@@ -1,25 +1,56 @@
-use crate::runtime::{Class, Object, Sel};
-use crate::{Encode, EncodeArguments};
-use super::MessageError;
+use std::fmt;
+
+use crate::runtime::{Class, Method, Object, Sel};
+use crate::{Encode, Encoding, EncodeArguments};
+
+pub enum VerificationError<'a> {
+    NilReceiver(Sel),
+    MethodNotFound(&'a Class, Sel),
+    MismatchedReturn(&'a Method, Encoding<'static>),
+    MismatchedArgumentsCount(&'a Method, usize),
+    MismatchedArgument(&'a Method, usize, Encoding<'static>),
+}
+
+impl<'a> fmt::Display for VerificationError<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            VerificationError::NilReceiver(sel) => {
+                write!(f, "Messsaging {:?} to nil", sel)
+            }
+            VerificationError::MethodNotFound(cls, sel) => {
+                write!(f, "Method {:?} not found on class {:?}", sel, cls)
+            }
+            VerificationError::MismatchedReturn(method, ret) => {
+                let expected_ret = method.return_type();
+                write!(f, "Return type code {} does not match expected {} for method {:?}",
+                    ret, expected_ret, method.name())
+            }
+            VerificationError::MismatchedArgumentsCount(method, count) => {
+                let expected_count = method.arguments_count();
+                write!(f, "Method {:?} accepts {} arguments, but {} were given",
+                    method.name(), expected_count, count)
+            }
+            VerificationError::MismatchedArgument(method, i, arg) => {
+                let expected = method.argument_type(i).unwrap();
+                write!(f, "Method {:?} expected argument at index {} with type code {:?} but was given {:?}",
+                    method.name(), i, expected, arg)
+            }
+        }
+    }
+}
 
 pub fn verify_message_signature<A, R>(cls: &Class, sel: Sel)
-        -> Result<(), MessageError>
+        -> Result<(), VerificationError>
         where A: EncodeArguments, R: Encode {
     let method = match cls.instance_method(sel) {
         Some(method) => method,
-        None => return Err(MessageError(
-            format!("Method {:?} not found on class {:?}",
-                sel, cls)
-        )),
+        None => return Err(VerificationError::MethodNotFound(cls, sel)),
     };
 
     let ret = R::ENCODING;
     let expected_ret = method.return_type();
     if ret != *expected_ret {
-        return Err(MessageError(
-            format!("Return type code {} does not match expected {} for method {:?}",
-                ret, expected_ret, method.name())
-        ));
+        return Err(VerificationError::MismatchedReturn(method, ret));
     }
 
     let self_and_cmd = [<*mut Object>::ENCODING, Sel::ENCODING];
@@ -28,19 +59,13 @@ pub fn verify_message_signature<A, R>(cls: &Class, sel: Sel)
     let count = self_and_cmd.len() + args.len();
     let expected_count = method.arguments_count();
     if count != expected_count {
-        return Err(MessageError(
-            format!("Method {:?} accepts {} arguments, but {} were given",
-                method.name(), expected_count, count)
-        ));
+        return Err(VerificationError::MismatchedArgumentsCount(method, count));
     }
 
-    for (i, arg) in self_and_cmd.iter().chain(args).enumerate() {
+    for (i, arg) in self_and_cmd.iter().chain(args).copied().enumerate() {
         let expected = method.argument_type(i).unwrap();
-        if *arg != *expected {
-            return Err(MessageError(
-                format!("Method {:?} expected argument at index {} with type code {:?} but was given {:?}",
-                    method.name(), i, expected, arg)
-            ));
+        if arg != *expected {
+            return Err(VerificationError::MismatchedArgument(method, i, arg));
         }
     }