Do not accept any return value for callbacks

It got added so we could keep using `s.pop_layer()` in single-line callbacks.
It was confusing, and the return value was ignored anyway.

examples/mines/main.rs

@@ -63,7 +63,7 @@ fn show_options(siv: &mut Cursive) {
                         new_game(s, *option);
                     }),
             )
-            .button("Back", |s| s.pop_layer()),
+            .dismiss_button("Back"),
     );
 }
 

examples/text_area.rs

@@ -41,8 +41,10 @@ fn main() {
                         ).unwrap();
                         find(s, &text);
                     })
-                    .button("Cancel", |s| s.pop_layer()),
+                    .dismiss_button("Cancel"),
-            ).on_event(Event::Key(Key::Esc), |s| s.pop_layer()),
+            ).on_event(Event::Key(Key::Esc), |s| {
+                s.pop_layer();
+            }),
         )
     });
 

src/event.rs

@@ -26,9 +26,9 @@ pub struct Callback(Rc<Box<Fn(&mut Cursive)>>);
 
 impl Callback {
     /// Wraps the given function into a `Callback` object.
-    pub fn from_fn<F, R>(f: F) -> Self
+    pub fn from_fn<F>(f: F) -> Self
     where
-        F: 'static + Fn(&mut Cursive) -> R,
+        F: 'static + Fn(&mut Cursive),
     {
         Callback(Rc::new(Box::new(move |siv| {
             f(siv);
@@ -77,9 +77,9 @@ pub enum EventResult {
 
 impl EventResult {
     /// Convenient method to create `Consumed(Some(f))`
-    pub fn with_cb<F, R>(f: F) -> Self
+    pub fn with_cb<F>(f: F) -> Self
     where
-        F: 'static + Fn(&mut Cursive) -> R,
+        F: 'static + Fn(&mut Cursive),
     {
         EventResult::Consumed(Some(Callback::from_fn(f)))
     }

src/view/any.rs

@@ -43,4 +43,3 @@ impl<T: View> AnyView for T {
         self
     }
 }
-

src/view/mod.rs

@@ -63,6 +63,6 @@ pub use self::position::{Offset, Position};
 pub use self::scroll::{ScrollBase, ScrollStrategy};
 pub use self::size_cache::SizeCache;
 pub use self::size_constraint::SizeConstraint;
+pub use self::view::View;
 pub use self::view_path::ViewPath;
 pub use self::view_wrapper::ViewWrapper;
-pub use self::view::View;

src/view/view.rs

@@ -5,7 +5,6 @@ use std::any::Any;
 use vec::Vec2;
 use view::{AnyView, Selector};
 
-
 /// Main trait defining a view behaviour.
 ///
 /// This is what you should implement to define a custom View.
@@ -86,4 +85,3 @@ pub trait View: Any + AnyView {
         false
     }
 }
-

src/views/button.rs

@@ -25,9 +25,9 @@ pub struct Button {
 
 impl Button {
     /// Creates a new button with the given content and callback.
-    pub fn new<F, R, S>(label: S, cb: F) -> Self
+    pub fn new<F, S>(label: S, cb: F) -> Self
     where
-        F: 'static + Fn(&mut Cursive) -> R,
+        F: 'static + Fn(&mut Cursive),
         S: Into<String>,
     {
         let label = label.into();
@@ -35,9 +35,9 @@ impl Button {
     }
 
     /// Creates a new button without angle brackets.
-    pub fn new_raw<F, R, S: Into<String>>(label: S, cb: F) -> Self
+    pub fn new_raw<F, S: Into<String>>(label: S, cb: F) -> Self
     where
-        F: 'static + Fn(&mut Cursive) -> R,
+        F: 'static + Fn(&mut Cursive),
     {
         Button {
             label: label.into(),

src/views/dialog.rs

@@ -30,9 +30,9 @@ struct ChildButton {
 }
 
 impl ChildButton {
-    pub fn new<F, R, S: Into<String>>(label: S, cb: F) -> Self
+    pub fn new<F, S: Into<String>>(label: S, cb: F) -> Self
     where
-        F: 'static + Fn(&mut Cursive) -> R,
+        F: 'static + Fn(&mut Cursive),
     {
         ChildButton {
             button: SizedView::new(Button::new(label, cb)),
@@ -151,9 +151,9 @@ impl Dialog {
     /// Adds a button to the dialog with the given label and callback.
     ///
     /// Consumes and returns self for easy chaining.
-    pub fn button<F, R, S: Into<String>>(mut self, label: S, cb: F) -> Self
+    pub fn button<F, S: Into<String>>(mut self, label: S, cb: F) -> Self
     where
-        F: 'static + Fn(&mut Cursive) -> R,
+        F: 'static + Fn(&mut Cursive),
     {
         self.buttons.push(ChildButton::new(label, cb));
 
@@ -184,7 +184,9 @@ impl Dialog {
 
     /// Shortcut method to add a button that will dismiss the dialog.
     pub fn dismiss_button<S: Into<String>>(self, label: S) -> Self {
-        self.button(label, |s| s.pop_layer())
+        self.button(label, |s| {
+            s.pop_layer();
+        })
     }
 
     /// Sets the title of the dialog.

src/views/menu_popup.rs

@@ -161,7 +161,9 @@ impl MenuPopup {
                             action_cb.clone()(s);
                         }
                     },
-                )).on_event(Key::Left, |s| s.pop_layer()),
+                )).on_event(Key::Left, |s| {
+                    s.pop_layer();
+                }),
             );
         })
     }

src/views/on_event_view.rs

@@ -80,10 +80,10 @@ impl<T: View> OnEventView<T> {
     /// Registers a callback when the given event is ignored by the child.
     ///
     /// Chainable variant.
-    pub fn on_event<F, R, E>(self, event: E, cb: F) -> Self
+    pub fn on_event<F, E>(self, event: E, cb: F) -> Self
     where
         E: Into<Event>,
-        F: 'static + Fn(&mut Cursive) -> R,
+        F: 'static + Fn(&mut Cursive),
     {
         self.with(|s| s.set_on_event(event, cb))
     }
@@ -93,10 +93,10 @@ impl<T: View> OnEventView<T> {
     /// The child will never receive this event.
     ///
     /// Chainable variant.
-    pub fn on_pre_event<F, R, E>(self, event: E, cb: F) -> Self
+    pub fn on_pre_event<F, E>(self, event: E, cb: F) -> Self
     where
         E: Into<Event>,
-        F: 'static + Fn(&mut Cursive) -> R,
+        F: 'static + Fn(&mut Cursive),
     {
         self.with(|s| s.set_on_pre_event(event, cb))
     }
@@ -135,10 +135,10 @@ impl<T: View> OnEventView<T> {
     }
 
     /// Registers a callback when the given event is ignored by the child.
-    pub fn set_on_event<F, R, E>(&mut self, event: E, cb: F)
+    pub fn set_on_event<F, E>(&mut self, event: E, cb: F)
     where
         E: Into<Event>,
-        F: Fn(&mut Cursive) -> R + 'static,
+        F: Fn(&mut Cursive) + 'static,
     {
         let cb = Callback::from_fn(cb);
         let action =
@@ -150,10 +150,10 @@ impl<T: View> OnEventView<T> {
     /// Registers a callback when the given event is received.
     ///
     /// The child will never receive this event.
-    pub fn set_on_pre_event<F, R, E>(&mut self, event: E, cb: F)
+    pub fn set_on_pre_event<F, E>(&mut self, event: E, cb: F)
     where
         E: Into<Event>,
-        F: 'static + Fn(&mut Cursive) -> R,
+        F: 'static + Fn(&mut Cursive),
     {
         let cb = Callback::from_fn(cb);
         // We want to clone the Callback every time we call the closure