Add Default trait impl for Lazy to enable struct field defaults (#167)

Author: dvaergiller

hypertext/src/alloc/mod.rs

@@ -312,6 +312,13 @@ impl<F: Fn(&mut Buffer<C>), C: Context> Debug for Lazy<F, C> {
     }
 }
 
+impl<C: Context> Default for Lazy<fn(&mut Buffer<C>), C> {
+    #[inline]
+    fn default() -> Lazy<fn(&mut Buffer<C>), C> {
+        Lazy::dangerously_create(|_| ())
+    }
+}
+
 /// A value rendered via its [`Display`] implementation.
 ///
 /// This will handle escaping special characters for you.

hypertext/tests/main.rs

@@ -3,7 +3,7 @@
 
 use std::fmt::{self, Display, Formatter};
 
-use hypertext::{Buffer, Raw, maud_borrow, maud_static, prelude::*, rsx_borrow, rsx_static};
+use hypertext::{Buffer, Lazy, Raw, maud_borrow, maud_static, prelude::*, rsx_borrow, rsx_static};
 
 #[test]
 fn readme() {
@@ -749,3 +749,46 @@ fn toggles() {
     );
     assert_eq!(rsx_result.as_inner(), r#"<input type="checkbox" checked>"#);
 }
+
+#[test]
+fn derive_default() {
+    #[derive(Default)]
+    struct Element<'a> {
+        pub id: &'a str,
+        pub tabindex: u32,
+        pub children: Lazy<fn(&mut Buffer)>,
+    }
+
+    impl<'a> Renderable for Element<'a> {
+        fn render_to(&self, buf: &mut Buffer) {
+            rsx! {
+                <div id=(self.id) tabindex=(self.tabindex)>
+                    (self.children)
+                </div>
+            }
+            .render_to(buf)
+        }
+    }
+
+    let with_children = rsx! {
+        <Element ..>
+          <h1>hello</h1>
+        </Element>
+    }
+    .render();
+
+    assert_eq!(
+        with_children.as_inner(),
+        r#"<div id="" tabindex="0"><h1>hello</h1></div>"#
+    );
+
+    let without_children = rsx! {
+        <Element ../>
+    }
+    .render();
+
+    assert_eq!(
+        without_children.as_inner(),
+        r#"<div id="" tabindex="0"></div>"#
+    );
+}