Added errprs.

.gitignore

@@ -1,4 +1,4 @@
 /target
 *.pyc
 *.swp
-
+*.swo

src/data/mod.rs

@@ -33,7 +33,7 @@ impl Table {
             None => {
                 self.fields.insert(name.to_string(), FieldDef::new());
                 Ok(())
-            },
+            }
         }
     }
 }
@@ -61,7 +61,7 @@ mod table {
         tbl.add_field("one", "id");
         match tbl.add_field("one", "id") {
             Ok(_) => unreachable!(" Should not duplicates."),
-            Err(_) => {},
+            Err(_) => {}
         }
     }
 }

src/error.rs

@@ -0,0 +1,51 @@
+use std::{error::Error, fmt};
+
+#[derive(Debug)]
+enum ErrorType {
+    TableAddFieldDuplicate(String),
+}
+
+impl fmt::Display for ErrorType {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            ErrorType::TableAddFieldDuplicate(data) => write!(f, "field '{}' already exists", data),
+        }
+    }
+}
+
+#[derive(Debug)]
+struct MTTError {
+    err: ErrorType,
+}
+
+impl MTTError {
+    fn new(err: ErrorType) -> Self {
+        Self { 
+            err: err,
+        }
+    }
+}
+
+impl Error for MTTError {}
+
+impl fmt::Display for MTTError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.err.to_string())
+    }
+}
+
+#[cfg(test)]
+mod errors {
+    use super::*;
+
+    #[test]
+    fn get_error() {
+        let err = MTTError::new(ErrorType::TableAddFieldDuplicate("tester".to_string()));
+        assert_eq!(err.to_string(), "field 'tester' already exists");
+        assert!(err.source().is_none());
+        let err = MTTError::new(ErrorType::TableAddFieldDuplicate("other".to_string()));
+        assert_eq!(err.to_string(), "field 'other' already exists");
+        assert!(err.source().is_none());
+    }
+}
+

src/lib.rs

@@ -1,5 +1,6 @@
 mod client;
 mod data;
+mod error;
 mod message;
 mod router;
 mod session;