Use a separate trait for object safety (#579)

This is relatively major change to the main trait's API. For context,
I always started from the concept of monomorphized traits, but later
several contributors asked about object safety. At that point I made
`Template` object-safe, and then even later added a `SizedTemplate`
to make some things easier for people who don't need object safety.

However, having object-safety in the primary trait is bad for
performance (a substantial number of calls into the virtual `Write`
trait is relatively slow), and I don't think those who don't need
object safety should pay for the cost of having it.

Additionally, I feel using associated consts for the extension and
size hint is more idiomatic than having accessor methods. I don't
know why I didn't use these from the start -- maybe associated
consts didn't exist yet, or I didn't yet know how/when to use them.
Askama is pretty old at this point...

1 files changed, 2 insertions, 3 deletions

diff --git a/askama_actix/src/lib.rs b/askama_actix/src/lib.rs
index 2496d92..baf9fd6 100644
--- a/askama_actix/src/lib.rs
+++ b/askama_actix/src/lib.rs
@@ -11,13 +11,12 @@ pub trait TemplateToResponse {
 
 impl<T: askama::Template> TemplateToResponse for T {
     fn to_response(&self) -> HttpResponse {
-        let mut buffer = BytesMut::with_capacity(self.size_hint());
+        let mut buffer = BytesMut::with_capacity(T::SIZE_HINT);
         if self.render_into(&mut buffer).is_err() {
             return ErrorInternalServerError("Template parsing error").error_response();
         }
 
-        let ctype =
-            askama::mime::extension_to_mime_type(self.extension().unwrap_or("txt")).to_string();
+        let ctype = askama::mime::extension_to_mime_type(T::EXTENSION.unwrap_or("txt")).to_string();
         HttpResponse::Ok()
             .content_type(ctype.as_str())
             .body(buffer.freeze())