down to 28e, sane ones

engine/src/output.rs

@@ -1,4 +1,5 @@
 use crate::*;
+use std::marker::PhantomData;
 //use std::sync::{Arc, Mutex, RwLock};
 
 /// Rendering target
@@ -42,54 +43,52 @@ impl<E: Engine, T: Content<E>> Content<E> for Option<T> {}
 
 impl<E: Engine, T: Content<E>> Content<E> for Vec<T> {}
 
+pub struct Thunk<E: Engine, T: Content<E>, F: Fn()->T + Send + Sync>(F, PhantomData<E>);
+
+impl<E: Engine, T: Content<E>, F: Fn()->T + Send + Sync> Thunk<E, T, F> {
+    pub fn new (thunk: F) -> Self {
+        Self(thunk, Default::default())
+    }
+}
+impl<E: Engine, T: Content<E>, F: Fn()->T + Send + Sync> Content<E> for Thunk<E, T, F> {
+    fn content (&self) -> impl Content<E> {
+        (self.0)()
+    }
+}
+
 #[macro_export] macro_rules! render {
     (($self:ident:$Struct:ty) => $content:expr) => {
         impl <E: Engine> Content<E> for $Struct {
-            fn content (&$self) -> Option<impl Content<E>> {
-                Some($content)
-            }
+            fn content (&$self) -> impl Content<E> { Some($content) }
         }
     };
     (|$self:ident:$Struct:ident $(<
-        $($L:lifetime),*
-        $($T:ident $(:$Trait:path)?),*
+        $($L:lifetime),* $($T:ident $(:$Trait:path)?),*
     >)?, $to:ident | $render:expr) => {
         impl <$($($L),*)? E: Engine, $($T$(:$Trait)?),*> Content<E>
         for $Struct $(<$($L),* $($T),*>>)? {
-            fn render (&$self, $to: &mut E::Output) {
-                Some($render)
-            }
+            fn render (&$self, $to: &mut E::Output) { $render }
         }
     };
     ($Engine:ty:
         ($self:ident:$Struct:ident $(<$(
-            $($L:lifetime)?
-            $($T:ident)?
-            $(:$Trait:path)?
+            $($L:lifetime)? $($T:ident)? $(:$Trait:path)?
         ),+>)?) => $content:expr
     ) => {
         impl $(<$($($L)? $($T)? $(:$Trait)?),+>)? Content<$Engine>
-        for $Struct $(<$($($L)? $($T)?),+>)?
-        {
-            fn content (&$self) -> Option<impl Content<$Engine>> {
-                Some($content)
-            }
+        for $Struct $(<$($($L)? $($T)?),+>)? {
+            fn content (&$self) -> impl Content<$Engine> { $content }
         }
     };
 
     ($Engine:ty:
         |$self:ident : $Struct:ident $(<$(
-            $($L:lifetime)?
-            $($T:ident)?
-            $(:$Trait:path)?
+            $($L:lifetime)? $($T:ident)? $(:$Trait:path)?
         ),+>)?, $to:ident| $render:expr
     ) => {
         impl $(<$($($L)? $($T)? $(:$Trait)?),+>)? Content<$Engine>
-        for $Struct $(<$($($L)? $($T)?),+>)?
-        {
-            fn render (&$self, $to: &mut <$Engine as Engine>::Output) {
-                Some($render)
-            }
+        for $Struct $(<$($($L)? $($T)?),+>)? {
+            fn render (&$self, $to: &mut <$Engine as Engine>::Output) { $render }
         }
     };
 }