Add Either widget

src/widget.rs

@@ -1,6 +1,6 @@
 use async_trait::async_trait;
 
-use crate::widgets::{Background, Border, Float, Padding, Layer};
+use crate::widgets::{Background, Border, Either, Float, Layer, Padding};
 use crate::{Frame, Size};
 
 // TODO Feature-gate these traits
@@ -37,6 +37,14 @@ pub trait WidgetExt: Sized {
         Border::new(self)
     }
 
+    fn first<W>(self) -> Either<Self, W> {
+        Either::First(self)
+    }
+
+    fn second<W>(self) -> Either<W, Self> {
+        Either::Second(self)
+    }
+
     fn float(self) -> Float<Self> {
         Float::new(self)
     }

src/widgets.rs

@@ -1,6 +1,7 @@
 mod background;
 mod border;
 mod cursor;
+mod either;
 mod empty;
 mod float;
 mod layer;
@@ -10,6 +11,7 @@ mod text;
 pub use background::*;
 pub use border::*;
 pub use cursor::*;
+pub use either::*;
 pub use empty::*;
 pub use float::*;
 pub use layer::*;

src/widgets/either.rs

@@ -0,0 +1,59 @@
+use async_trait::async_trait;
+
+use crate::{AsyncWidget, Frame, Size, Widget};
+
+pub enum Either<I1, I2> {
+    First(I1),
+    Second(I2),
+}
+
+impl<E, I1, I2> Widget<E> for Either<I1, I2>
+where
+    I1: Widget<E>,
+    I2: Widget<E>,
+{
+    fn size(
+        &self,
+        frame: &mut Frame,
+        max_width: Option<u16>,
+        max_height: Option<u16>,
+    ) -> Result<Size, E> {
+        match self {
+            Self::First(l) => l.size(frame, max_width, max_height),
+            Self::Second(r) => r.size(frame, max_width, max_height),
+        }
+    }
+
+    fn draw(self, frame: &mut Frame) -> Result<(), E> {
+        match self {
+            Self::First(l) => l.draw(frame),
+            Self::Second(r) => r.draw(frame),
+        }
+    }
+}
+
+#[async_trait]
+impl<E, I1, I2> AsyncWidget<E> for Either<I1, I2>
+where
+    I1: AsyncWidget<E> + Send + Sync,
+    I2: AsyncWidget<E> + Send + Sync,
+{
+    async fn size(
+        &self,
+        frame: &mut Frame,
+        max_width: Option<u16>,
+        max_height: Option<u16>,
+    ) -> Result<Size, E> {
+        match self {
+            Self::First(l) => l.size(frame, max_width, max_height).await,
+            Self::Second(r) => r.size(frame, max_width, max_height).await,
+        }
+    }
+
+    async fn draw(self, frame: &mut Frame) -> Result<(), E> {
+        match self {
+            Self::First(l) => l.draw(frame).await,
+            Self::Second(r) => r.draw(frame).await,
+        }
+    }
+}