impl RenderOnce on tuples of up to 8 values

sailfish/src/runtime/render.rs

@@ -131,10 +131,7 @@ pub trait RenderOnce: Sized {
 //     }
 // }
 
-impl<T> RenderOnce for T
-where
-    T: Render,
-{
+impl<T: Render> RenderOnce for T {
     #[inline]
     fn render_once(self, b: &mut Buffer) -> Result<(), RenderError> {
         self.render(b)
@@ -459,6 +456,69 @@ impl<T: Render> Render for Wrapping<T> {
     }
 }
 
+macro_rules! render_tuple {
+    ($A:ident) => {
+        render_tuple!(@ $A);
+    };
+    ($A:ident $(, $T:ident)+) => {
+        render_tuple!(@ $A $(, $T)+);
+        render_tuple!($($T),+);
+    };
+    (@ $($T:ident),*) => {
+    	impl<$($T: Render),+> Render for ($($T,)+) {
+     		#[inline]
+            fn render(&self, b: &mut Buffer) -> Result<(), RenderError> {
+            	#[allow(non_snake_case)]
+            	let ($($T,)+) = self;
+                $($T.render(b)?;)+
+                Ok(())
+            }
+
+            #[inline]
+            fn render_escaped(&self, b: &mut Buffer) -> Result<(), RenderError> {
+            	#[allow(non_snake_case)]
+            	let ($($T,)+) = self;
+             	$($T.render_escaped(b)?;)+
+              	Ok(())
+            }
+        }
+    };
+}
+
+macro_rules! render_once_tuple {
+    ($A:ident) => {
+        render_once_tuple!(@ $A);
+    };
+    ($A:ident $(, $T:ident)+) => {
+        render_once_tuple!(@ $A $(, $T)+);
+        render_once_tuple!($($T),+);
+    };
+    (@ $($T:ident),*) => {
+    impl<$($T: RenderOnce),+> RenderOnce for ($($T,)+) {
+     		#[inline]
+            fn render_once(self, b: &mut Buffer) -> Result<(), RenderError> {
+            	#[allow(non_snake_case)]
+            	let ($($T,)+) = self;
+                $($T.render_once(b)?;)+
+                Ok(())
+            }
+
+            #[inline]
+            fn render_once_escaped(self, b: &mut Buffer) -> Result<(), RenderError> {
+            	#[allow(non_snake_case)]
+            	let ($($T,)+) = self;
+             	$($T.render_once_escaped(b)?;)+
+              	Ok(())
+            }
+        }
+    };
+}
+
+// TODO: figure out how to use specialization to allow a Render impl on tuples, if possible. If
+// 		 not, oh well, it can be worked around.
+// render_tuple!(A, B, C, D, E, F, G, H);
+render_once_tuple!(A, B, C, D, E, F, G, H);
+
 /// The error type which is returned from template function
 #[derive(Clone, Debug)]
 pub enum RenderError {