`std::fmt::String` impls.

src/reader.rs

@@ -1,6 +1,7 @@
 use std::io::{Buffer, Reader, IoError};
 use std::num::{cast, NumCast};
 use std::error::{Error, FromError};
+use std::fmt;
 
 use rustc_serialize::Decoder;
 
@@ -12,6 +13,17 @@ pub struct InvalidEncoding {
     detail: Option<String>,
 }
 
+impl fmt::String for InvalidEncoding {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            InvalidEncoding { detail: None, desc } =>
+                write!(fmt, "{}", desc),
+            InvalidEncoding { detail: Some(ref detail), desc } =>
+                write!(fmt, "{} ({})", desc, detail)
+        }
+    }
+}
+
 /// An error that can be produced during decoding.
 ///
 /// If decoding from a Buffer, assume that the buffer has been left
@@ -31,6 +43,19 @@ pub enum DecodingError {
     SizeLimit
 }
 
+impl fmt::String for DecodingError {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            DecodingError::IoError(ref ioerr) =>
+                write!(fmt, "IoError: {}", ioerr),
+            DecodingError::InvalidEncoding(ref ib) =>
+                write!(fmt, "InvalidEncoding: {}", ib),
+            DecodingError::SizeLimit =>
+                write!(fmt, "SizeLimit")
+        }
+    }
+}
+
 pub type DecodingResult<T> = Result<T, DecodingError>;
 
 fn wrap_io(err: IoError) -> DecodingError {