Improve IntoAsciiStrError

Author: tormol

src/ascii_str.rs

@@ -365,7 +365,34 @@ pub struct IntoAsciiStrError {
     /// If less than 128, it was a byte >= 128
     not_ascii: char,
 }
-
+impl IntoAsciiStrError {
+    /// The index of the first non-ASCII byte or character.
+    pub fn index(self) -> usize {
+        self.index
+    }
+    /// Get the byte that caused the error.
+    ///
+    /// If a str was being converted, the first byte in the utf8 encoding is returned.
+    pub fn byte(self) -> u8 {
+        if (self.not_ascii as u32) < 128 {
+            self.not_ascii as u8 + 128
+        } else {
+            // char::encode_utf8() is unstable
+            let mut s = String::with_capacity(4);
+            s.push(self.not_ascii);
+            s.bytes().next().unwrap()
+        }
+    }
+    /// Get the char that caused conversions from a `str` to fail.
+    ///
+    /// Returns `None` if the error was caused by a byte in a `[u8]`
+    pub fn char(self) -> Option<char> {
+        match self.not_ascii as u32 {
+            0...127 => None, // byte in [u8]
+               _    => Some(self.not_ascii),
+        }
+    }
+}
 impl fmt::Debug for IntoAsciiStrError {
     fn fmt(&self,  fmtr: &mut fmt::Formatter) -> fmt::Result {
         if (self.not_ascii as u32) < 128 {
@@ -386,7 +413,11 @@ impl fmt::Display for IntoAsciiStrError {
 }
 impl Error for IntoAsciiStrError {
     fn description(&self) -> &'static str {
-        "one or more bytes (or chars if str) are not ASCII"
+        if (self.not_ascii as u32) < 128 {
+            "one or more bytes are not ASCII"
+        } else {
+            "one or more characters are not ASCII"
+        }
     }
 }