Add Callback::from_fn_mut

Cursive::add_global_callback now takes a FnMut

src/cursive.rs

@@ -514,12 +514,12 @@ impl Cursive {
     /// ```
     pub fn add_global_callback<F, E: Into<Event>>(&mut self, event: E, cb: F)
     where
-        F: Fn(&mut Cursive) + 'static,
+        F: FnMut(&mut Cursive) + 'static,
     {
         self.global_callbacks
             .entry(event.into())
             .or_insert_with(Vec::new)
-            .push(Callback::from_fn(cb));
+            .push(Callback::from_fn_mut(cb));
     }
 
     /// Removes any callback tied to the given event.

src/event.rs

@@ -14,6 +14,7 @@
 //!   table is checked.
 
 use std::any::Any;
+use std::cell::RefCell;
 use std::ops::Deref;
 use std::rc::Rc;
 use vec::Vec2;
@@ -39,6 +40,22 @@ impl Callback {
         })))
     }
 
+    /// Wrap a `FnMut` into a `Callback` object.
+    ///
+    /// If this methods tries to call itself, nested calls will be no-ops.
+    pub fn from_fn_mut<F>(f: F) -> Self
+    where
+        F: 'static + FnMut(&mut Cursive),
+    {
+        let cb = RefCell::new(f);
+
+        Self::from_fn(move |s| {
+            if let Ok(mut cb) = cb.try_borrow_mut() {
+                (&mut *cb)(s);
+            }
+        })
+    }
+
     /// Returns a dummy callback that doesn't run anything.
     pub fn dummy() -> Self {
         Callback::from_fn(|_| ())