Relaxed Sized bound on Box/Rc/Arc/Cow for ToSql

* Fix Box<T> for unsized

* refactoring

* Add more tests

* ?Sized for Cow, Rc, Arc too

src/types/to_sql.rs

@@ -87,37 +87,27 @@ pub trait ToSql {
     fn to_sql(&self) -> Result<ToSqlOutput<'_>>;
 }
 
-impl ToSql for Box<dyn ToSql> {
+impl<T: ToSql + Clone + ?Sized> ToSql for Cow<'_, T> {
-    fn to_sql(&self) -> Result<ToSqlOutput<'_>> {
-        let derefed: &dyn ToSql = &**self;
-        derefed.to_sql()
-    }
-}
-
-impl<T: ToSql + Clone> ToSql for Cow<'_, T> {
     fn to_sql(&self) -> Result<ToSqlOutput<'_>> {
         self.as_ref().to_sql()
     }
 }
 
-impl<T: ToSql> ToSql for Box<T> {
+impl<T: ToSql + ?Sized> ToSql for Box<T> {
     fn to_sql(&self) -> Result<ToSqlOutput<'_>> {
-        let derefed: &dyn ToSql = &**self;
+        self.as_ref().to_sql()
-        derefed.to_sql()
     }
 }
 
-impl<T: ToSql> ToSql for std::rc::Rc<T> {
+impl<T: ToSql + ?Sized> ToSql for std::rc::Rc<T> {
     fn to_sql(&self) -> Result<ToSqlOutput<'_>> {
-        let derefed: &dyn ToSql = &**self;
+        self.as_ref().to_sql()
-        derefed.to_sql()
     }
 }
 
-impl<T: ToSql> ToSql for std::sync::Arc<T> {
+impl<T: ToSql + ?Sized> ToSql for std::sync::Arc<T> {
     fn to_sql(&self) -> Result<ToSqlOutput<'_>> {
-        let derefed: &dyn ToSql = &**self;
+        self.as_ref().to_sql()
-        derefed.to_sql()
     }
 }
 
@@ -239,13 +229,29 @@ mod test {
     }
 
     #[test]
-    fn test_box() {
+    fn test_box_dyn() {
+        let s: Box<dyn ToSql> = Box::new("Hello world!");
+        let r = ToSql::to_sql(&s);
+
+        assert!(r.is_ok());
+    }
+
+    #[test]
+    fn test_box_deref() {
         let s: Box<str> = "Hello world!".into();
         let r = s.to_sql();
 
         assert!(r.is_ok());
     }
 
+    #[test]
+    fn test_box_direct() {
+        let s: Box<str> = "Hello world!".into();
+        let r = ToSql::to_sql(&s);
+
+        assert!(r.is_ok());
+    }
+
     #[test]
     fn test_cells() {
         use std::{rc::Rc, sync::Arc};