Implement ToSql for &'a T where T: ToSql

This allows more flexible use of ToSql in generic contexts by allowing
references to be used for encoding.

src/types/mod.rs

@@ -815,6 +815,25 @@ pub trait ToSql: fmt::Debug {
                       -> Result<IsNull>;
 }
 
+impl<'a, T> ToSql for &'a T where T: ToSql {
+    fn to_sql_checked(&self, ty: &Type, out: &mut Write, ctx: &SessionInfo)
+                      -> Result<IsNull> {
+        if !<&'a T as ToSql>::accepts(ty) {
+            return Err(Error::WrongType(ty.clone()));
+        }
+        self.to_sql(ty, out, ctx)
+    }
+
+
+    fn to_sql<W: Write + ?Sized>(&self, ty: &Type, out: &mut W, ctx: &SessionInfo) -> Result<IsNull> {
+        (*self).to_sql(ty, out, ctx)
+    }
+
+    fn accepts(ty: &Type) -> bool { T::accepts(ty) }
+}
+
+
+
 impl<T: ToSql> ToSql for Option<T> {
     to_sql_checked!();
 

tests/types/mod.rs

@@ -31,6 +31,14 @@ fn test_type<T: PartialEq+FromSql+ToSql, S: fmt::Display>(sql_type: &str, checks
     }
 }
 
+#[test]
+fn test_ref_tosql() {
+    let conn = or_panic!(Connection::connect("postgres://postgres@localhost", &SslMode::None));
+    let stmt = conn.prepare("SELECT $1::Int").unwrap();
+    let num: &ToSql = &&7;
+    stmt.query(&[num]).unwrap();
+}
+
 #[test]
 fn test_bool_params() {
     test_type("BOOL", &[(Some(true), "'t'"), (Some(false), "'f'"),