diff --git a/gstreamer-rtsp-server/src/rtsp_session_pool.rs b/gstreamer-rtsp-server/src/rtsp_session_pool.rs
index edf5d937b..1ff1b935c 100644
--- a/gstreamer-rtsp-server/src/rtsp_session_pool.rs
+++ b/gstreamer-rtsp-server/src/rtsp_session_pool.rs
@@ -9,25 +9,26 @@ use std::cell::RefCell;
 use std::mem::transmute;
 use RTSPSessionPool;
 
-unsafe extern "C" fn trampoline_watch(
+unsafe extern "C" fn trampoline_watch<F: FnMut(&RTSPSessionPool) -> Continue + Send + 'static>(
     pool: *mut ffi::GstRTSPSessionPool,
     func: gpointer,
 ) -> gboolean {
     #[cfg_attr(feature = "cargo-clippy", allow(transmute_ptr_to_ref))]
-    let func: &RefCell<Box<FnMut(&RTSPSessionPool) -> Continue + Send + 'static>> = transmute(func);
+    let func: &RefCell<F> = transmute(func);
     (&mut *func.borrow_mut())(&from_glib_borrow(pool)).to_glib()
 }
 
-unsafe extern "C" fn destroy_closure_watch(ptr: gpointer) {
-    Box::<RefCell<Box<FnMut(&RTSPSessionPool) -> Continue + Send + 'static>>>::from_raw(
-        ptr as *mut _,
-    );
+unsafe extern "C" fn destroy_closure_watch<
+    F: FnMut(&RTSPSessionPool) -> Continue + Send + 'static,
+>(
+    ptr: gpointer,
+) {
+    Box::<RefCell<F>>::from_raw(ptr as *mut _);
 }
 
 fn into_raw_watch<F: FnMut(&RTSPSessionPool) -> Continue + Send + 'static>(func: F) -> gpointer {
     #[cfg_attr(feature = "cargo-clippy", allow(type_complexity))]
-    let func: Box<RefCell<Box<FnMut(&RTSPSessionPool) -> Continue + Send + 'static>>> =
-        Box::new(RefCell::new(Box::new(func)));
+    let func: Box<RefCell<F>> = Box::new(RefCell::new(func));
     Box::into_raw(func) as gpointer
 }
 
@@ -55,12 +56,11 @@ impl<O: IsA<RTSPSessionPool>> RTSPSessionPoolExtManual for O {
         skip_assert_initialized!();
         unsafe {
             let source = ffi::gst_rtsp_session_pool_create_watch(self.as_ref().to_glib_none().0);
-            let trampoline = trampoline_watch as gpointer;
             glib_ffi::g_source_set_callback(
                 source,
-                Some(transmute(trampoline)),
+                Some(transmute(trampoline_watch::<F> as usize)),
                 into_raw_watch(func),
-                Some(destroy_closure_watch),
+                Some(destroy_closure_watch::<F>),
             );
             glib_ffi::g_source_set_priority(source, priority.to_glib());
 
diff --git a/gstreamer-video/src/functions.rs b/gstreamer-video/src/functions.rs
index ead7dc9ca..3865d2a09 100644
--- a/gstreamer-video/src/functions.rs
+++ b/gstreamer-video/src/functions.rs
@@ -55,7 +55,7 @@ pub fn convert_sample_async<F>(
         F: FnOnce(Result<gst::Sample, glib::Error>) + Send + 'static,
     {
         #[cfg_attr(feature = "cargo-clippy", allow(transmute_ptr_to_ref))]
-        let callback: &mut Option<Box<F>> = mem::transmute(user_data);
+        let callback: &mut Option<F> = mem::transmute(user_data);
         let callback = callback.take().unwrap();
 
         if error.is_null() {
@@ -68,11 +68,11 @@ pub fn convert_sample_async<F>(
     where
         F: FnOnce(Result<gst::Sample, glib::Error>) + Send + 'static,
     {
-        let _: Box<Option<Box<F>>> = Box::from_raw(user_data as *mut _);
+        let _: Box<Option<F>> = Box::from_raw(user_data as *mut _);
     }
 
     unsafe {
-        let user_data: Box<Option<Box<F>>> = Box::new(Some(Box::new(func)));
+        let user_data: Box<Option<F>> = Box::new(Some(func));
 
         ffi::gst_video_convert_sample_async(
             sample.to_glib_none().0,
diff --git a/gstreamer/src/bus.rs b/gstreamer/src/bus.rs
index cc12b8993..6fd533ac6 100644
--- a/gstreamer/src/bus.rs
+++ b/gstreamer/src/bus.rs
@@ -20,36 +20,39 @@ use Bus;
 use BusSyncReply;
 use Message;
 
-unsafe extern "C" fn trampoline_watch(
+unsafe extern "C" fn trampoline_watch<F: FnMut(&Bus, &Message) -> Continue + Send + 'static>(
     bus: *mut ffi::GstBus,
     msg: *mut ffi::GstMessage,
     func: gpointer,
 ) -> gboolean {
     #[cfg_attr(feature = "cargo-clippy", allow(transmute_ptr_to_ref))]
-    let func: &RefCell<Box<FnMut(&Bus, &Message) -> Continue + Send + 'static>> = transmute(func);
+    let func: &RefCell<F> = transmute(func);
     (&mut *func.borrow_mut())(&from_glib_borrow(bus), &Message::from_glib_borrow(msg)).to_glib()
 }
 
-unsafe extern "C" fn destroy_closure_watch(ptr: gpointer) {
-    Box::<RefCell<Box<FnMut(&Bus, &Message) -> Continue + Send + 'static>>>::from_raw(
-        ptr as *mut _,
-    );
+unsafe extern "C" fn destroy_closure_watch<
+    F: FnMut(&Bus, &Message) -> Continue + Send + 'static,
+>(
+    ptr: gpointer,
+) {
+    Box::<RefCell<F>>::from_raw(ptr as *mut _);
 }
 
 fn into_raw_watch<F: FnMut(&Bus, &Message) -> Continue + Send + 'static>(func: F) -> gpointer {
     #[cfg_attr(feature = "cargo-clippy", allow(type_complexity))]
-    let func: Box<RefCell<Box<FnMut(&Bus, &Message) -> Continue + Send + 'static>>> =
-        Box::new(RefCell::new(Box::new(func)));
+    let func: Box<RefCell<F>> = Box::new(RefCell::new(func));
     Box::into_raw(func) as gpointer
 }
 
-unsafe extern "C" fn trampoline_sync(
+unsafe extern "C" fn trampoline_sync<
+    F: Fn(&Bus, &Message) -> BusSyncReply + Send + Sync + 'static,
+>(
     bus: *mut ffi::GstBus,
     msg: *mut ffi::GstMessage,
     func: gpointer,
 ) -> ffi::GstBusSyncReply {
     #[cfg_attr(feature = "cargo-clippy", allow(transmute_ptr_to_ref))]
-    let f: &&(Fn(&Bus, &Message) -> BusSyncReply + Send + Sync + 'static) = transmute(func);
+    let f: &F = transmute(func);
     let res = f(&from_glib_borrow(bus), &Message::from_glib_borrow(msg)).to_glib();
 
     if res == ffi::GST_BUS_DROP {
@@ -59,15 +62,18 @@ unsafe extern "C" fn trampoline_sync(
     res
 }
 
-unsafe extern "C" fn destroy_closure_sync(ptr: gpointer) {
-    Box::<Box<Fn(&Bus, &Message) -> BusSyncReply + Send + Sync + 'static>>::from_raw(ptr as *mut _);
+unsafe extern "C" fn destroy_closure_sync<
+    F: Fn(&Bus, &Message) -> BusSyncReply + Send + Sync + 'static,
+>(
+    ptr: gpointer,
+) {
+    Box::<F>::from_raw(ptr as *mut _);
 }
 
 fn into_raw_sync<F: Fn(&Bus, &Message) -> BusSyncReply + Send + Sync + 'static>(
     func: F,
 ) -> gpointer {
-    let func: Box<Box<Fn(&Bus, &Message) -> BusSyncReply + Send + Sync + 'static>> =
-        Box::new(Box::new(func));
+    let func: Box<F> = Box::new(func);
     Box::into_raw(func) as gpointer
 }
 
@@ -90,12 +96,11 @@ impl Bus {
         skip_assert_initialized!();
         unsafe {
             let source = ffi::gst_bus_create_watch(self.to_glib_none().0);
-            let trampoline = trampoline_watch as gpointer;
             glib_ffi::g_source_set_callback(
                 source,
-                Some(transmute(trampoline)),
+                Some(transmute(trampoline_watch::<F> as usize)),
                 into_raw_watch(func),
-                Some(destroy_closure_watch),
+                Some(destroy_closure_watch::<F>),
             );
             glib_ffi::g_source_set_priority(source, priority.to_glib());
 
@@ -116,9 +121,9 @@ impl Bus {
             from_glib(ffi::gst_bus_add_watch_full(
                 self.to_glib_none().0,
                 glib_ffi::G_PRIORITY_DEFAULT,
-                Some(trampoline_watch),
+                Some(trampoline_watch::<F>),
                 into_raw_watch(func),
-                Some(destroy_closure_watch),
+                Some(destroy_closure_watch::<F>),
             ))
         }
     }
@@ -130,9 +135,9 @@ impl Bus {
         unsafe {
             ffi::gst_bus_set_sync_handler(
                 self.to_glib_none().0,
-                Some(trampoline_sync),
+                Some(trampoline_sync::<F>),
                 into_raw_sync(func),
-                Some(destroy_closure_sync),
+                Some(destroy_closure_sync::<F>),
             )
         }
     }
diff --git a/gstreamer/src/clock.rs b/gstreamer/src/clock.rs
index 9eef70b17..4e6795950 100644
--- a/gstreamer/src/clock.rs
+++ b/gstreamer/src/clock.rs
@@ -33,14 +33,14 @@ glib_wrapper! {
     }
 }
 
-unsafe extern "C" fn trampoline_wait_async(
+unsafe extern "C" fn trampoline_wait_async<F: Fn(&Clock, ClockTime, &ClockId) + Send + 'static>(
     clock: *mut ffi::GstClock,
     time: ffi::GstClockTime,
     id: gpointer,
     func: gpointer,
 ) -> gboolean {
     #[cfg_attr(feature = "cargo-clippy", allow(transmute_ptr_to_ref))]
-    let f: &&(Fn(&Clock, ClockTime, &ClockId) + Send + 'static) = transmute(func);
+    let f: &F = transmute(func);
     f(
         &from_glib_borrow(clock),
         from_glib(time),
@@ -49,13 +49,17 @@ unsafe extern "C" fn trampoline_wait_async(
     glib_ffi::GTRUE
 }
 
-unsafe extern "C" fn destroy_closure_wait_async(ptr: gpointer) {
-    Box::<Box<Fn(&Clock, ClockTime, &ClockId) + Send + 'static>>::from_raw(ptr as *mut _);
+unsafe extern "C" fn destroy_closure_wait_async<
+    F: Fn(&Clock, ClockTime, &ClockId) + Send + 'static,
+>(
+    ptr: gpointer,
+) {
+    Box::<F>::from_raw(ptr as *mut _);
 }
 
 fn into_raw_wait_async<F: Fn(&Clock, ClockTime, &ClockId) + Send + 'static>(func: F) -> gpointer {
     #[cfg_attr(feature = "cargo-clippy", allow(type_complexity))]
-    let func: Box<Box<Fn(&Clock, ClockTime, &ClockId) + Send + 'static>> = Box::new(Box::new(func));
+    let func: Box<F> = Box::new(func);
     Box::into_raw(func) as gpointer
 }
 
@@ -84,9 +88,9 @@ impl ClockId {
         let ret: ClockReturn = unsafe {
             from_glib(ffi::gst_clock_id_wait_async(
                 self.to_glib_none().0,
-                Some(trampoline_wait_async),
+                Some(trampoline_wait_async::<F>),
                 into_raw_wait_async(func),
-                Some(destroy_closure_wait_async),
+                Some(destroy_closure_wait_async::<F>),
             ))
         };
         ret.into_result()
diff --git a/gstreamer/src/element.rs b/gstreamer/src/element.rs
index 3de91cbc3..4ea7f79ec 100644
--- a/gstreamer/src/element.rs
+++ b/gstreamer/src/element.rs
@@ -652,13 +652,13 @@ impl<O: IsA<Element>> ElementExtManual for O {
     where
         F: FnOnce(&Self) + Send + 'static,
     {
-        let user_data: Box<Option<Box<F>>> = Box::new(Some(Box::new(func)));
+        let user_data: Box<Option<F>> = Box::new(Some(func));
 
         unsafe extern "C" fn trampoline<O: IsA<Element>, F: FnOnce(&O) + Send + 'static>(
             element: *mut ffi::GstElement,
             user_data: glib_ffi::gpointer,
         ) {
-            let user_data: &mut Option<Box<F>> = &mut *(user_data as *mut _);
+            let user_data: &mut Option<F> = &mut *(user_data as *mut _);
             let callback = user_data.take().unwrap();
 
             callback(&Element::from_glib_borrow(element).unsafe_cast());
@@ -667,17 +667,15 @@ impl<O: IsA<Element>> ElementExtManual for O {
         unsafe extern "C" fn free_user_data<O: IsA<Element>, F: FnOnce(&O) + Send + 'static>(
             user_data: glib_ffi::gpointer,
         ) {
-            let _: Box<Option<Box<F>>> = Box::from_raw(user_data as *mut _);
+            let _: Box<Option<F>> = Box::from_raw(user_data as *mut _);
         }
 
-        let trampoline = trampoline::<Self, F>;
-        let free_user_data = free_user_data::<Self, F>;
         unsafe {
             ffi::gst_element_call_async(
                 self.as_ref().to_glib_none().0,
-                Some(trampoline),
+                Some(trampoline::<Self, F>),
                 Box::into_raw(user_data) as *mut _,
-                Some(free_user_data),
+                Some(free_user_data::<Self, F>),
             );
         }
     }
diff --git a/gstreamer/src/iterator.rs b/gstreamer/src/iterator.rs
index 1d70ad322..65c9c73c9 100644
--- a/gstreamer/src/iterator.rs
+++ b/gstreamer/src/iterator.rs
@@ -90,12 +90,7 @@ where
             mem::forget(self);
 
             let func_box: Box<Fn(T) -> bool + Send + Sync + 'static> = Box::new(func);
-            // FIXME: Use Value::from_type once we depend on new enough GLib
-            let mut closure_value = glib::Value::uninitialized();
-            gobject_ffi::g_value_init(
-                closure_value.to_glib_none_mut().0,
-                filter_boxed_get_type::<T>(),
-            );
+            let mut closure_value = glib::Value::from_type(from_glib(filter_boxed_get_type::<T>()));
             gobject_ffi::g_value_set_boxed(
                 closure_value.to_glib_none_mut().0,
                 Arc::into_raw(Arc::new(func_box)) as gpointer,
@@ -117,12 +112,11 @@ where
             let mut elem = glib::Value::uninitialized();
 
             let mut func = func;
-            let func_obj: &mut (FnMut(T) -> bool) = &mut func;
-            let func_ptr = &func_obj as *const &mut (FnMut(T) -> bool) as gpointer;
+            let func_ptr = &mut func as *mut F as gpointer;
 
             let res = from_glib(ffi::gst_iterator_find_custom(
                 self.to_glib_none_mut().0,
-                Some(find_trampoline::<T>),
+                Some(find_trampoline::<T, F>),
                 elem.to_glib_none_mut().0,
                 func_ptr,
             ));
@@ -140,12 +134,11 @@ where
     {
         unsafe {
             let mut func = func;
-            let func_obj: &mut (FnMut(T)) = &mut func;
-            let func_ptr = &func_obj as *const &mut (FnMut(T)) as gpointer;
+            let func_ptr = &mut func as *mut F as gpointer;
 
             let res = ffi::gst_iterator_foreach(
                 self.to_glib_none_mut().0,
-                Some(foreach_trampoline::<T>),
+                Some(foreach_trampoline::<T, F>),
                 func_ptr,
             );
 
@@ -163,13 +156,10 @@ where
     {
         unsafe {
             let mut func = func;
-            let func_obj: &mut (FnMut(U, T) -> Result<U, U>) = &mut func;
-            let func_ptr = &func_obj as *const &mut (FnMut(U, T) -> Result<U, U>) as gpointer;
+            let func_ptr = &mut func as *mut F as gpointer;
 
             let mut accum = Some(init);
-            // FIXME: Use Value::from_type once we depend on new enough GLib
-            let mut ret = glib::Value::uninitialized();
-            gobject_ffi::g_value_init(ret.to_glib_none_mut().0, gobject_ffi::G_TYPE_POINTER);
+            let mut ret = glib::Value::from_type(glib::Type::Pointer);
             gobject_ffi::g_value_set_pointer(
                 ret.to_glib_none_mut().0,
                 &mut accum as *mut _ as gpointer,
@@ -177,7 +167,7 @@ where
 
             let res = ffi::gst_iterator_fold(
                 self.to_glib_none_mut().0,
-                Some(fold_trampoline::<T, U>),
+                Some(fold_trampoline::<T, U, F>),
                 ret.to_glib_none_mut().0,
                 func_ptr,
             );
@@ -405,13 +395,16 @@ unsafe extern "C" fn filter_boxed_get_type<T: StaticType + 'static>() -> glib_ff
     TYPE
 }
 
-unsafe extern "C" fn find_trampoline<T>(value: gconstpointer, func: gconstpointer) -> i32
+unsafe extern "C" fn find_trampoline<T, F: FnMut(T) -> bool>(
+    value: gconstpointer,
+    func: gconstpointer,
+) -> i32
 where
     for<'a> T: FromValueOptional<'a> + 'static,
 {
     let value = value as *const gobject_ffi::GValue;
 
-    let func = func as *mut &mut (FnMut(T) -> bool);
+    let func = func as *mut F;
     let value = &*(value as *const glib::Value);
     let value = value.get::<T>().unwrap();
 
@@ -422,18 +415,20 @@ where
     }
 }
 
-unsafe extern "C" fn foreach_trampoline<T>(value: *const gobject_ffi::GValue, func: gpointer)
-where
+unsafe extern "C" fn foreach_trampoline<T, F: FnMut(T)>(
+    value: *const gobject_ffi::GValue,
+    func: gpointer,
+) where
     for<'a> T: FromValueOptional<'a> + 'static,
 {
-    let func = func as *mut &mut (FnMut(T));
+    let func = func as *mut F;
     let value = &*(value as *const glib::Value);
     let value = value.get::<T>().unwrap();
 
     (*func)(value);
 }
 
-unsafe extern "C" fn fold_trampoline<T, U>(
+unsafe extern "C" fn fold_trampoline<T, U, F: FnMut(U, T) -> Result<U, U>>(
     value: *const gobject_ffi::GValue,
     ret: *mut gobject_ffi::GValue,
     func: gpointer,
@@ -441,7 +436,7 @@ unsafe extern "C" fn fold_trampoline<T, U>(
 where
     for<'a> T: FromValueOptional<'a> + 'static,
 {
-    let func = func as *mut &mut (FnMut(U, T) -> Result<U, U>);
+    let func = func as *mut F;
     let value = &*(value as *const glib::Value);
     let value = value.get::<T>().unwrap();
 
diff --git a/gstreamer/src/pad.rs b/gstreamer/src/pad.rs
index e27b0529a..d56d9d9ea 100644
--- a/gstreamer/src/pad.rs
+++ b/gstreamer/src/pad.rs
@@ -35,10 +35,10 @@ use std::mem::transmute;
 use std::ptr;
 
 use glib;
-use glib::object::IsA;
+use glib::object::{Cast, IsA};
 use glib::translate::{
-    from_glib, from_glib_borrow, from_glib_full, from_glib_none, mut_override, FromGlib, ToGlib,
-    ToGlibPtr,
+    from_glib, from_glib_borrow, from_glib_full, from_glib_none, mut_override, FromGlib,
+    FromGlibPtrBorrow, ToGlib, ToGlibPtr,
 };
 use glib::StaticType;
 use glib_ffi;
@@ -116,7 +116,7 @@ impl Drop for StreamLock {
 pub trait PadExtManual: 'static {
     fn add_probe<F>(&self, mask: PadProbeType, func: F) -> Option<PadProbeId>
     where
-        F: Fn(&Pad, &mut PadProbeInfo) -> PadProbeReturn + Send + Sync + 'static;
+        F: Fn(&Self, &mut PadProbeInfo) -> PadProbeReturn + Send + Sync + 'static;
     fn remove_probe(&self, id: PadProbeId);
 
     fn chain(&self, buffer: Buffer) -> Result<FlowSuccess, FlowError>;
@@ -165,65 +165,65 @@ pub trait PadExtManual: 'static {
 
     fn set_activate_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>) -> Result<(), LoggableError> + Send + Sync + 'static;
+        F: Fn(&Self, &Option<::Object>) -> Result<(), LoggableError> + Send + Sync + 'static;
 
     fn set_activatemode_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>, ::PadMode, bool) -> Result<(), LoggableError>
+        F: Fn(&Self, &Option<::Object>, ::PadMode, bool) -> Result<(), LoggableError>
             + Send
             + Sync
             + 'static;
 
     fn set_chain_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>, ::Buffer) -> Result<FlowSuccess, FlowError>
+        F: Fn(&Self, &Option<::Object>, ::Buffer) -> Result<FlowSuccess, FlowError>
             + Send
             + Sync
             + 'static;
 
     fn set_chain_list_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>, ::BufferList) -> Result<FlowSuccess, FlowError>
+        F: Fn(&Self, &Option<::Object>, ::BufferList) -> Result<FlowSuccess, FlowError>
             + Send
             + Sync
             + 'static;
 
     fn set_event_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>, ::Event) -> bool + Send + Sync + 'static;
+        F: Fn(&Self, &Option<::Object>, ::Event) -> bool + Send + Sync + 'static;
 
     fn set_event_full_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>, ::Event) -> Result<FlowSuccess, FlowError>
+        F: Fn(&Self, &Option<::Object>, ::Event) -> Result<FlowSuccess, FlowError>
             + Send
             + Sync
             + 'static;
 
     fn set_getrange_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>, u64, u32) -> Result<::Buffer, ::FlowError>
+        F: Fn(&Self, &Option<::Object>, u64, u32) -> Result<::Buffer, ::FlowError>
             + Send
             + Sync
             + 'static;
 
     fn set_iterate_internal_links_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>) -> ::Iterator<Pad> + Send + Sync + 'static;
+        F: Fn(&Self, &Option<::Object>) -> ::Iterator<Pad> + Send + Sync + 'static;
 
     fn set_link_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>, &Pad) -> Result<::PadLinkSuccess, ::PadLinkError>
+        F: Fn(&Self, &Option<::Object>, &Pad) -> Result<::PadLinkSuccess, ::PadLinkError>
             + Send
             + Sync
             + 'static;
 
     fn set_query_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>, &mut ::QueryRef) -> bool + Send + Sync + 'static;
+        F: Fn(&Self, &Option<::Object>, &mut ::QueryRef) -> bool + Send + Sync + 'static;
 
     fn set_unlink_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>) + Send + Sync + 'static;
+        F: Fn(&Self, &Option<::Object>) + Send + Sync + 'static;
 
     fn start_task<F: FnMut() + Send + 'static>(&self, func: F) -> Result<(), glib::BoolError>;
 
@@ -272,18 +272,16 @@ pub trait PadExtManual: 'static {
 impl<O: IsA<Pad>> PadExtManual for O {
     fn add_probe<F>(&self, mask: PadProbeType, func: F) -> Option<PadProbeId>
     where
-        F: Fn(&Pad, &mut PadProbeInfo) -> PadProbeReturn + Send + Sync + 'static,
+        F: Fn(&Self, &mut PadProbeInfo) -> PadProbeReturn + Send + Sync + 'static,
     {
         unsafe {
-            let func_box: Box<
-                Fn(&Pad, &mut PadProbeInfo) -> PadProbeReturn + Send + Sync + 'static,
-            > = Box::new(func);
+            let func_box: Box<F> = Box::new(func);
             let id = ffi::gst_pad_add_probe(
                 self.as_ref().to_glib_none().0,
                 mask.to_glib(),
-                Some(trampoline_pad_probe),
-                Box::into_raw(Box::new(func_box)) as gpointer,
-                Some(destroy_closure),
+                Some(trampoline_pad_probe::<Self, F>),
+                Box::into_raw(func_box) as gpointer,
+                Some(destroy_closure::<F>),
             );
 
             if id == 0 {
@@ -517,224 +515,185 @@ impl<O: IsA<Pad>> PadExtManual for O {
 
     fn set_activate_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>) -> Result<(), LoggableError> + Send + Sync + 'static,
+        F: Fn(&Self, &Option<::Object>) -> Result<(), LoggableError> + Send + Sync + 'static,
     {
         #[cfg_attr(feature = "cargo-clippy", allow(type_complexity))]
         unsafe {
-            let func_box: Box<
-                Fn(&Pad, &Option<::Object>) -> Result<(), LoggableError> + Send + Sync + 'static,
-            > = Box::new(func);
+            let func_box: Box<F> = Box::new(func);
             ffi::gst_pad_set_activate_function_full(
                 self.as_ref().to_glib_none().0,
-                Some(trampoline_activate_function),
-                Box::into_raw(Box::new(func_box)) as gpointer,
-                Some(destroy_closure),
+                Some(trampoline_activate_function::<Self, F>),
+                Box::into_raw(func_box) as gpointer,
+                Some(destroy_closure::<F>),
             );
         }
     }
 
     fn set_activatemode_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>, ::PadMode, bool) -> Result<(), LoggableError>
+        F: Fn(&Self, &Option<::Object>, ::PadMode, bool) -> Result<(), LoggableError>
             + Send
             + Sync
             + 'static,
     {
         #[cfg_attr(feature = "cargo-clippy", allow(type_complexity))]
         unsafe {
-            let func_box: Box<
-                Fn(&Pad, &Option<::Object>, ::PadMode, bool) -> Result<(), LoggableError>
-                    + Send
-                    + Sync
-                    + 'static,
-            > = Box::new(func);
+            let func_box: Box<F> = Box::new(func);
             ffi::gst_pad_set_activatemode_function_full(
                 self.as_ref().to_glib_none().0,
-                Some(trampoline_activatemode_function),
-                Box::into_raw(Box::new(func_box)) as gpointer,
-                Some(destroy_closure),
+                Some(trampoline_activatemode_function::<Self, F>),
+                Box::into_raw(func_box) as gpointer,
+                Some(destroy_closure::<F>),
             );
         }
     }
 
     fn set_chain_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>, ::Buffer) -> Result<FlowSuccess, FlowError>
+        F: Fn(&Self, &Option<::Object>, ::Buffer) -> Result<FlowSuccess, FlowError>
             + Send
             + Sync
             + 'static,
     {
         unsafe {
-            let func_box: Box<
-                Fn(&Pad, &Option<::Object>, ::Buffer) -> Result<FlowSuccess, FlowError>
-                    + Send
-                    + Sync
-                    + 'static,
-            > = Box::new(func);
+            let func_box: Box<F> = Box::new(func);
             ffi::gst_pad_set_chain_function_full(
                 self.as_ref().to_glib_none().0,
-                Some(trampoline_chain_function),
-                Box::into_raw(Box::new(func_box)) as gpointer,
-                Some(destroy_closure),
+                Some(trampoline_chain_function::<Self, F>),
+                Box::into_raw(func_box) as gpointer,
+                Some(destroy_closure::<F>),
             );
         }
     }
 
     fn set_chain_list_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>, ::BufferList) -> Result<FlowSuccess, FlowError>
+        F: Fn(&Self, &Option<::Object>, ::BufferList) -> Result<FlowSuccess, FlowError>
             + Send
             + Sync
             + 'static,
     {
         unsafe {
-            let func_box: Box<
-                Fn(&Pad, &Option<::Object>, ::BufferList) -> Result<FlowSuccess, FlowError>
-                    + Send
-                    + Sync
-                    + 'static,
-            > = Box::new(func);
+            let func_box: Box<F> = Box::new(func);
             ffi::gst_pad_set_chain_list_function_full(
                 self.as_ref().to_glib_none().0,
-                Some(trampoline_chain_list_function),
-                Box::into_raw(Box::new(func_box)) as gpointer,
-                Some(destroy_closure),
+                Some(trampoline_chain_list_function::<Self, F>),
+                Box::into_raw(func_box) as gpointer,
+                Some(destroy_closure::<F>),
             );
         }
     }
 
     fn set_event_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>, ::Event) -> bool + Send + Sync + 'static,
+        F: Fn(&Self, &Option<::Object>, ::Event) -> bool + Send + Sync + 'static,
     {
         unsafe {
-            let func_box: Box<
-                Fn(&Pad, &Option<::Object>, ::Event) -> bool + Send + Sync + 'static,
-            > = Box::new(func);
+            let func_box: Box<F> = Box::new(func);
             ffi::gst_pad_set_event_function_full(
                 self.as_ref().to_glib_none().0,
-                Some(trampoline_event_function),
-                Box::into_raw(Box::new(func_box)) as gpointer,
-                Some(destroy_closure),
+                Some(trampoline_event_function::<Self, F>),
+                Box::into_raw(func_box) as gpointer,
+                Some(destroy_closure::<F>),
             );
         }
     }
 
     fn set_event_full_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>, ::Event) -> Result<FlowSuccess, FlowError>
+        F: Fn(&Self, &Option<::Object>, ::Event) -> Result<FlowSuccess, FlowError>
             + Send
             + Sync
             + 'static,
     {
         unsafe {
-            let func_box: Box<
-                Fn(&Pad, &Option<::Object>, ::Event) -> Result<FlowSuccess, FlowError>
-                    + Send
-                    + Sync
-                    + 'static,
-            > = Box::new(func);
+            let func_box: Box<F> = Box::new(func);
             ffi::gst_pad_set_event_full_function_full(
                 self.as_ref().to_glib_none().0,
-                Some(trampoline_event_full_function),
-                Box::into_raw(Box::new(func_box)) as gpointer,
-                Some(destroy_closure),
+                Some(trampoline_event_full_function::<Self, F>),
+                Box::into_raw(func_box) as gpointer,
+                Some(destroy_closure::<F>),
             );
         }
     }
 
     fn set_getrange_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>, u64, u32) -> Result<::Buffer, FlowError>
+        F: Fn(&Self, &Option<::Object>, u64, u32) -> Result<::Buffer, FlowError>
             + Send
             + Sync
             + 'static,
     {
         unsafe {
-            #[cfg_attr(feature = "cargo-clippy", allow(type_complexity))]
-            let func_box: Box<
-                Fn(&Pad, &Option<::Object>, u64, u32) -> Result<::Buffer, FlowError>
-                    + Send
-                    + Sync
-                    + 'static,
-            > = Box::new(func);
+            let func_box: Box<F> = Box::new(func);
             ffi::gst_pad_set_getrange_function_full(
                 self.as_ref().to_glib_none().0,
-                Some(trampoline_getrange_function),
-                Box::into_raw(Box::new(func_box)) as gpointer,
-                Some(destroy_closure),
+                Some(trampoline_getrange_function::<Self, F>),
+                Box::into_raw(func_box) as gpointer,
+                Some(destroy_closure::<F>),
             );
         }
     }
 
     fn set_iterate_internal_links_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>) -> ::Iterator<Pad> + Send + Sync + 'static,
+        F: Fn(&Self, &Option<::Object>) -> ::Iterator<Pad> + Send + Sync + 'static,
     {
         unsafe {
-            let func_box: Box<
-                Fn(&Pad, &Option<::Object>) -> ::Iterator<Pad> + Send + Sync + 'static,
-            > = Box::new(func);
+            let func_box: Box<F> = Box::new(func);
             ffi::gst_pad_set_iterate_internal_links_function_full(
                 self.as_ref().to_glib_none().0,
-                Some(trampoline_iterate_internal_links_function),
-                Box::into_raw(Box::new(func_box)) as gpointer,
-                Some(destroy_closure),
+                Some(trampoline_iterate_internal_links_function::<Self, F>),
+                Box::into_raw(func_box) as gpointer,
+                Some(destroy_closure::<F>),
             );
         }
     }
 
     fn set_link_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>, &Pad) -> Result<::PadLinkSuccess, ::PadLinkError>
+        F: Fn(&Self, &Option<::Object>, &Pad) -> Result<::PadLinkSuccess, ::PadLinkError>
             + Send
             + Sync
             + 'static,
     {
         unsafe {
-            let func_box: Box<
-                Fn(&Pad, &Option<::Object>, &Pad) -> Result<::PadLinkSuccess, ::PadLinkError>
-                    + Send
-                    + Sync
-                    + 'static,
-            > = Box::new(func);
+            let func_box: Box<F> = Box::new(func);
             ffi::gst_pad_set_link_function_full(
                 self.as_ref().to_glib_none().0,
-                Some(trampoline_link_function),
-                Box::into_raw(Box::new(func_box)) as gpointer,
-                Some(destroy_closure),
+                Some(trampoline_link_function::<Self, F>),
+                Box::into_raw(func_box) as gpointer,
+                Some(destroy_closure::<F>),
             );
         }
     }
 
     fn set_query_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>, &mut ::QueryRef) -> bool + Send + Sync + 'static,
+        F: Fn(&Self, &Option<::Object>, &mut ::QueryRef) -> bool + Send + Sync + 'static,
     {
         unsafe {
-            let func_box: Box<
-                Fn(&Pad, &Option<::Object>, &mut ::QueryRef) -> bool + Send + Sync + 'static,
-            > = Box::new(func);
+            let func_box: Box<F> = Box::new(func);
             ffi::gst_pad_set_query_function_full(
                 self.as_ref().to_glib_none().0,
-                Some(trampoline_query_function),
-                Box::into_raw(Box::new(func_box)) as gpointer,
-                Some(destroy_closure),
+                Some(trampoline_query_function::<Self, F>),
+                Box::into_raw(func_box) as gpointer,
+                Some(destroy_closure::<F>),
             );
         }
     }
 
     fn set_unlink_function<F>(&self, func: F)
     where
-        F: Fn(&Pad, &Option<::Object>) + Send + Sync + 'static,
+        F: Fn(&Self, &Option<::Object>) + Send + Sync + 'static,
     {
         unsafe {
-            let func_box: Box<Fn(&Pad, &Option<::Object>) + Send + Sync + 'static> = Box::new(func);
+            let func_box: Box<F> = Box::new(func);
             ffi::gst_pad_set_unlink_function_full(
                 self.as_ref().to_glib_none().0,
-                Some(trampoline_unlink_function),
-                Box::into_raw(Box::new(func_box)) as gpointer,
-                Some(destroy_closure),
+                Some(trampoline_unlink_function::<Self, F>),
+                Box::into_raw(func_box) as gpointer,
+                Some(destroy_closure::<F>),
             );
         }
     }
@@ -744,9 +703,9 @@ impl<O: IsA<Pad>> PadExtManual for O {
             glib_result_from_gboolean!(
                 ffi::gst_pad_start_task(
                     self.as_ref().to_glib_none().0,
-                    Some(trampoline_pad_task),
+                    Some(trampoline_pad_task::<F>),
                     into_raw_pad_task(func),
-                    Some(destroy_closure_pad_task),
+                    Some(destroy_closure::<F>),
                 ),
                 "Failed to start pad task",
             )
@@ -1039,14 +998,19 @@ impl<O: IsA<Pad>> PadExtManual for O {
     }
 }
 
-unsafe extern "C" fn trampoline_pad_probe(
+unsafe extern "C" fn trampoline_pad_probe<
+    T,
+    F: Fn(&T, &mut PadProbeInfo) -> PadProbeReturn + Send + Sync + 'static,
+>(
     pad: *mut ffi::GstPad,
     info: *mut ffi::GstPadProbeInfo,
     func: gpointer,
-) -> ffi::GstPadProbeReturn {
+) -> ffi::GstPadProbeReturn
+where
+    T: IsA<Pad>,
+{
     #[cfg_attr(feature = "cargo-clippy", allow(transmute_ptr_to_ref))]
-    let func: &&(Fn(&Pad, &mut PadProbeInfo) -> PadProbeReturn + Send + Sync + 'static) =
-        transmute(func);
+    let func: &F = transmute(func);
     let mut data_type = None;
 
     let mut probe_info = PadProbeInfo {
@@ -1085,7 +1049,7 @@ unsafe extern "C" fn trampoline_pad_probe(
         },
     };
 
-    let ret = func(&from_glib_borrow(pad), &mut probe_info).to_glib();
+    let ret = func(&Pad::from_glib_borrow(pad).unsafe_cast(), &mut probe_info).to_glib();
 
     match probe_info.data {
         Some(PadProbeData::Buffer(buffer)) => {
@@ -1115,68 +1079,78 @@ unsafe extern "C" fn trampoline_pad_probe(
     ret
 }
 
-unsafe extern "C" fn trampoline_activate_function(
+unsafe extern "C" fn trampoline_activate_function<
+    T,
+    F: Fn(&T, &Option<::Object>) -> Result<(), LoggableError> + Send + Sync + 'static,
+>(
     pad: *mut ffi::GstPad,
     parent: *mut ffi::GstObject,
-) -> glib_ffi::gboolean {
+) -> glib_ffi::gboolean
+where
+    T: IsA<Pad>,
+{
     #[cfg_attr(feature = "cargo-clippy", allow(transmute_ptr_to_ref))]
-    let func: &&(Fn(&Pad, &Option<::Object>) -> Result<(), LoggableError>
-           + Send
-           + Sync
-           + 'static) = transmute((*pad).activatedata);
+    let func: &F = transmute((*pad).activatedata);
 
-    let pad: Pad = from_glib_borrow(pad);
-    match func(&pad, &from_glib_borrow(parent)) {
+    match func(
+        &Pad::from_glib_borrow(pad).unsafe_cast(),
+        &from_glib_borrow(parent),
+    ) {
         Ok(()) => true,
         Err(err) => {
-            err.log_with_object(&pad);
+            err.log_with_object(&Pad::from_glib_borrow(pad));
             false
         }
     }
     .to_glib()
 }
 
-unsafe extern "C" fn trampoline_activatemode_function(
+unsafe extern "C" fn trampoline_activatemode_function<
+    T,
+    F: Fn(&T, &Option<::Object>, ::PadMode, bool) -> Result<(), LoggableError> + Send + Sync + 'static,
+>(
     pad: *mut ffi::GstPad,
     parent: *mut ffi::GstObject,
     mode: ffi::GstPadMode,
     active: glib_ffi::gboolean,
-) -> glib_ffi::gboolean {
+) -> glib_ffi::gboolean
+where
+    T: IsA<Pad>,
+{
     #[cfg_attr(feature = "cargo-clippy", allow(transmute_ptr_to_ref))]
-    let func: &&(Fn(&Pad, &Option<::Object>, ::PadMode, bool) -> Result<(), LoggableError>
-           + Send
-           + Sync
-           + 'static) = transmute((*pad).activatemodedata);
+    let func: &F = transmute((*pad).activatemodedata);
 
-    let pad: Pad = from_glib_borrow(pad);
     match func(
-        &pad,
+        &&Pad::from_glib_borrow(pad).unsafe_cast(),
         &from_glib_borrow(parent),
         from_glib(mode),
         from_glib(active),
     ) {
         Ok(()) => true,
         Err(err) => {
-            err.log_with_object(&pad);
+            err.log_with_object(&Pad::from_glib_borrow(pad));
             false
         }
     }
     .to_glib()
 }
 
-unsafe extern "C" fn trampoline_chain_function(
+unsafe extern "C" fn trampoline_chain_function<
+    T,
+    F: Fn(&T, &Option<::Object>, ::Buffer) -> Result<FlowSuccess, FlowError> + Send + Sync + 'static,
+>(
     pad: *mut ffi::GstPad,
     parent: *mut ffi::GstObject,
     buffer: *mut ffi::GstBuffer,
-) -> ffi::GstFlowReturn {
+) -> ffi::GstFlowReturn
+where
+    T: IsA<Pad>,
+{
     #[cfg_attr(feature = "cargo-clippy", allow(transmute_ptr_to_ref))]
-    let func: &&(Fn(&Pad, &Option<::Object>, ::Buffer) -> Result<FlowSuccess, FlowError>
-           + Send
-           + Sync
-           + 'static) = transmute((*pad).chaindata);
+    let func: &F = transmute((*pad).chaindata);
 
     let res: FlowReturn = func(
-        &from_glib_borrow(pad),
+        &Pad::from_glib_borrow(pad).unsafe_cast(),
         &from_glib_borrow(parent),
         from_glib_full(buffer),
     )
@@ -1184,19 +1158,25 @@ unsafe extern "C" fn trampoline_chain_function(
     res.to_glib()
 }
 
-unsafe extern "C" fn trampoline_chain_list_function(
+unsafe extern "C" fn trampoline_chain_list_function<
+    T,
+    F: Fn(&T, &Option<::Object>, ::BufferList) -> Result<FlowSuccess, FlowError>
+        + Send
+        + Sync
+        + 'static,
+>(
     pad: *mut ffi::GstPad,
     parent: *mut ffi::GstObject,
     list: *mut ffi::GstBufferList,
-) -> ffi::GstFlowReturn {
+) -> ffi::GstFlowReturn
+where
+    T: IsA<Pad>,
+{
     #[cfg_attr(feature = "cargo-clippy", allow(transmute_ptr_to_ref))]
-    let func: &&(Fn(&Pad, &Option<::Object>, ::BufferList) -> Result<FlowSuccess, FlowError>
-           + Send
-           + Sync
-           + 'static) = transmute((*pad).chainlistdata);
+    let func: &F = transmute((*pad).chainlistdata);
 
     let res: FlowReturn = func(
-        &from_glib_borrow(pad),
+        &Pad::from_glib_borrow(pad).unsafe_cast(),
         &from_glib_borrow(parent),
         from_glib_full(list),
     )
@@ -1204,36 +1184,44 @@ unsafe extern "C" fn trampoline_chain_list_function(
     res.to_glib()
 }
 
-unsafe extern "C" fn trampoline_event_function(
+unsafe extern "C" fn trampoline_event_function<
+    T,
+    F: Fn(&T, &Option<::Object>, ::Event) -> bool + Send + Sync + 'static,
+>(
     pad: *mut ffi::GstPad,
     parent: *mut ffi::GstObject,
     event: *mut ffi::GstEvent,
-) -> glib_ffi::gboolean {
+) -> glib_ffi::gboolean
+where
+    T: IsA<Pad>,
+{
     #[cfg_attr(feature = "cargo-clippy", allow(transmute_ptr_to_ref))]
-    let func: &&(Fn(&Pad, &Option<::Object>, ::Event) -> bool + Send + Sync + 'static) =
-        transmute((*pad).eventdata);
+    let func: &F = transmute((*pad).eventdata);
 
     func(
-        &from_glib_borrow(pad),
+        &Pad::from_glib_borrow(pad).unsafe_cast(),
         &from_glib_borrow(parent),
         from_glib_full(event),
     )
     .to_glib()
 }
 
-unsafe extern "C" fn trampoline_event_full_function(
+unsafe extern "C" fn trampoline_event_full_function<
+    T,
+    F: Fn(&T, &Option<::Object>, ::Event) -> Result<FlowSuccess, FlowError> + Send + Sync + 'static,
+>(
     pad: *mut ffi::GstPad,
     parent: *mut ffi::GstObject,
     event: *mut ffi::GstEvent,
-) -> ffi::GstFlowReturn {
+) -> ffi::GstFlowReturn
+where
+    T: IsA<Pad>,
+{
     #[cfg_attr(feature = "cargo-clippy", allow(transmute_ptr_to_ref))]
-    let func: &&(Fn(&Pad, &Option<::Object>, ::Event) -> Result<FlowSuccess, FlowError>
-           + Send
-           + Sync
-           + 'static) = transmute((*pad).eventdata);
+    let func: &F = transmute((*pad).eventdata);
 
     let res: FlowReturn = func(
-        &from_glib_borrow(pad),
+        &Pad::from_glib_borrow(pad).unsafe_cast(),
         &from_glib_borrow(parent),
         from_glib_full(event),
     )
@@ -1241,21 +1229,24 @@ unsafe extern "C" fn trampoline_event_full_function(
     res.to_glib()
 }
 
-unsafe extern "C" fn trampoline_getrange_function(
+unsafe extern "C" fn trampoline_getrange_function<
+    T,
+    F: Fn(&T, &Option<::Object>, u64, u32) -> Result<::Buffer, FlowError> + Send + Sync + 'static,
+>(
     pad: *mut ffi::GstPad,
     parent: *mut ffi::GstObject,
     offset: u64,
     length: u32,
     buffer: *mut *mut ffi::GstBuffer,
-) -> ffi::GstFlowReturn {
+) -> ffi::GstFlowReturn
+where
+    T: IsA<Pad>,
+{
     #[cfg_attr(feature = "cargo-clippy", allow(transmute_ptr_to_ref))]
-    let func: &&(Fn(&Pad, &Option<::Object>, u64, u32) -> Result<::Buffer, FlowError>
-           + Send
-           + Sync
-           + 'static) = transmute((*pad).getrangedata);
+    let func: &F = transmute((*pad).getrangedata);
 
     match func(
-        &from_glib_borrow(pad),
+        &Pad::from_glib_borrow(pad).unsafe_cast(),
         &from_glib_borrow(parent),
         offset,
         length,
@@ -1268,39 +1259,49 @@ unsafe extern "C" fn trampoline_getrange_function(
     }
 }
 
-unsafe extern "C" fn trampoline_iterate_internal_links_function(
+unsafe extern "C" fn trampoline_iterate_internal_links_function<
+    T,
+    F: Fn(&T, &Option<::Object>) -> ::Iterator<Pad> + Send + Sync + 'static,
+>(
     pad: *mut ffi::GstPad,
     parent: *mut ffi::GstObject,
-) -> *mut ffi::GstIterator {
+) -> *mut ffi::GstIterator
+where
+    T: IsA<Pad>,
+{
     #[cfg_attr(feature = "cargo-clippy", allow(transmute_ptr_to_ref))]
-    let func: &&(Fn(&Pad, &Option<::Object>) -> ::Iterator<Pad> + Send + Sync + 'static) =
-        transmute((*pad).iterintlinkdata);
+    let func: &F = transmute((*pad).iterintlinkdata);
 
     // Steal the iterator and return it
-    let ret = func(&from_glib_borrow(pad), &from_glib_borrow(parent));
+    let ret = func(
+        &Pad::from_glib_borrow(pad).unsafe_cast(),
+        &from_glib_borrow(parent),
+    );
     let ptr = ret.to_glib_none().0;
     mem::forget(ret);
 
     ptr as *mut _
 }
 
-unsafe extern "C" fn trampoline_link_function(
+unsafe extern "C" fn trampoline_link_function<
+    T,
+    F: Fn(&T, &Option<::Object>, &::Pad) -> Result<::PadLinkSuccess, ::PadLinkError>
+        + Send
+        + Sync
+        + 'static,
+>(
     pad: *mut ffi::GstPad,
     parent: *mut ffi::GstObject,
     peer: *mut ffi::GstPad,
-) -> ffi::GstPadLinkReturn {
+) -> ffi::GstPadLinkReturn
+where
+    T: IsA<Pad>,
+{
     #[cfg_attr(feature = "cargo-clippy", allow(transmute_ptr_to_ref))]
-    let func: &&(Fn(
-        &Pad,
-        &Option<::Object>,
-        &::Pad,
-    ) -> Result<::PadLinkSuccess, ::PadLinkError>
-           + Send
-           + Sync
-           + 'static) = transmute((*pad).linkdata);
+    let func: &F = transmute((*pad).linkdata);
 
     let res: ::PadLinkReturn = func(
-        &from_glib_borrow(pad),
+        &Pad::from_glib_borrow(pad).unsafe_cast(),
         &from_glib_borrow(parent),
         &from_glib_borrow(peer),
     )
@@ -1308,51 +1309,59 @@ unsafe extern "C" fn trampoline_link_function(
     res.to_glib()
 }
 
-unsafe extern "C" fn trampoline_query_function(
+unsafe extern "C" fn trampoline_query_function<
+    T,
+    F: Fn(&T, &Option<::Object>, &mut ::QueryRef) -> bool + Send + Sync + 'static,
+>(
     pad: *mut ffi::GstPad,
     parent: *mut ffi::GstObject,
     query: *mut ffi::GstQuery,
-) -> glib_ffi::gboolean {
+) -> glib_ffi::gboolean
+where
+    T: IsA<Pad>,
+{
     #[cfg_attr(feature = "cargo-clippy", allow(transmute_ptr_to_ref))]
-    let func: &&(Fn(&Pad, &Option<::Object>, &mut ::QueryRef) -> bool + Send + Sync + 'static) =
-        transmute((*pad).querydata);
+    let func: &F = transmute((*pad).querydata);
 
     func(
-        &from_glib_borrow(pad),
+        &Pad::from_glib_borrow(pad).unsafe_cast(),
         &from_glib_borrow(parent),
         ::QueryRef::from_mut_ptr(query),
     )
     .to_glib()
 }
 
-unsafe extern "C" fn trampoline_unlink_function(
+unsafe extern "C" fn trampoline_unlink_function<
+    T,
+    F: Fn(&T, &Option<::Object>) + Send + Sync + 'static,
+>(
     pad: *mut ffi::GstPad,
     parent: *mut ffi::GstObject,
-) {
+) where
+    T: IsA<Pad>,
+{
     #[cfg_attr(feature = "cargo-clippy", allow(transmute_ptr_to_ref))]
-    let func: &&(Fn(&Pad, &Option<::Object>) + Send + Sync + 'static) =
-        transmute((*pad).unlinkdata);
+    let func: &F = transmute((*pad).unlinkdata);
 
-    func(&from_glib_borrow(pad), &from_glib_borrow(parent))
+    func(
+        &Pad::from_glib_borrow(pad).unsafe_cast(),
+        &from_glib_borrow(parent),
+    )
 }
 
-unsafe extern "C" fn destroy_closure(ptr: gpointer) {
-    Box::<Box<Fn()>>::from_raw(ptr as *mut _);
+unsafe extern "C" fn destroy_closure<F>(ptr: gpointer) {
+    Box::<F>::from_raw(ptr as *mut _);
 }
 
-unsafe extern "C" fn trampoline_pad_task(func: gpointer) {
+unsafe extern "C" fn trampoline_pad_task<F: FnMut() + Send + 'static>(func: gpointer) {
     #[cfg_attr(feature = "cargo-clippy", allow(transmute_ptr_to_ref))]
-    let func: &RefCell<Box<FnMut() + Send + 'static>> = transmute(func);
+    let func: &RefCell<F> = transmute(func);
     (&mut *func.borrow_mut())()
 }
 
-unsafe extern "C" fn destroy_closure_pad_task(ptr: gpointer) {
-    Box::<RefCell<Box<FnMut() + Send + 'static>>>::from_raw(ptr as *mut _);
-}
-
 fn into_raw_pad_task<F: FnMut() + Send + 'static>(func: F) -> gpointer {
     #[cfg_attr(feature = "cargo-clippy", allow(type_complexity))]
-    let func: Box<RefCell<Box<FnMut() + Send + 'static>>> = Box::new(RefCell::new(Box::new(func)));
+    let func: Box<RefCell<F>> = Box::new(RefCell::new(func));
     Box::into_raw(func) as gpointer
 }
 
diff --git a/gstreamer/src/promise.rs b/gstreamer/src/promise.rs
index b2500d9ce..8f19d23f2 100644
--- a/gstreamer/src/promise.rs
+++ b/gstreamer/src/promise.rs
@@ -36,13 +36,13 @@ impl Promise {
     where
         F: FnOnce(&Promise) + Send + 'static,
     {
-        let user_data: Box<Option<Box<F>>> = Box::new(Some(Box::new(func)));
+        let user_data: Box<Option<F>> = Box::new(Some(func));
 
         unsafe extern "C" fn trampoline<F: FnOnce(&Promise) + Send + 'static>(
             promise: *mut ffi::GstPromise,
             user_data: glib_ffi::gpointer,
         ) {
-            let user_data: &mut Option<Box<F>> = &mut *(user_data as *mut _);
+            let user_data: &mut Option<F> = &mut *(user_data as *mut _);
             let callback = user_data.take().unwrap();
 
             callback(&from_glib_borrow(promise));
@@ -51,16 +51,14 @@ impl Promise {
         unsafe extern "C" fn free_user_data<F: FnOnce(&Promise) + Send + 'static>(
             user_data: glib_ffi::gpointer,
         ) {
-            let _: Box<Option<Box<F>>> = Box::from_raw(user_data as *mut _);
+            let _: Box<Option<F>> = Box::from_raw(user_data as *mut _);
         }
 
-        let trampoline = trampoline::<F>;
-        let free_user_data = free_user_data::<F>;
         unsafe {
             from_glib_full(ffi::gst_promise_new_with_change_func(
-                Some(trampoline),
+                Some(trampoline::<F>),
                 Box::into_raw(user_data) as *mut _,
-                Some(free_user_data),
+                Some(free_user_data::<F>),
             ))
         }
     }
diff --git a/gstreamer/src/typefind.rs b/gstreamer/src/typefind.rs
index e0414f794..98133852d 100644
--- a/gstreamer/src/typefind.rs
+++ b/gstreamer/src/typefind.rs
@@ -56,19 +56,18 @@ impl<'a> TypeFind<'a> {
         let extensions = extensions.into();
         let possible_caps = possible_caps.into();
         unsafe {
-            let func: Box<Box<Fn(&mut TypeFind) + Send + Sync + 'static>> =
-                Box::new(Box::new(func));
+            let func: Box<F> = Box::new(func);
             let func = Box::into_raw(func);
 
             let res = ffi::gst_type_find_register(
                 plugin.to_glib_none().0,
                 name.to_glib_none().0,
                 rank,
-                Some(type_find_trampoline),
+                Some(type_find_trampoline::<F>),
                 extensions.to_glib_none().0,
                 possible_caps.to_glib_none().0,
                 func as *mut _,
-                Some(type_find_closure_drop),
+                Some(type_find_closure_drop::<F>),
             );
 
             glib_result_from_gboolean!(res, "Failed to register typefind factory")
@@ -116,17 +115,19 @@ impl TypeFindFactory {
     }
 }
 
-unsafe extern "C" fn type_find_trampoline(
+unsafe extern "C" fn type_find_trampoline<F: Fn(&mut TypeFind) + Send + Sync + 'static>(
     find: *mut ffi::GstTypeFind,
     user_data: glib_ffi::gpointer,
 ) {
     #[cfg_attr(feature = "cargo-clippy", allow(transmute_ptr_to_ref))]
-    let func: &&(Fn(&mut TypeFind) + Send + Sync + 'static) = mem::transmute(user_data);
+    let func: &F = mem::transmute(user_data);
     func(&mut *(find as *mut TypeFind));
 }
 
-unsafe extern "C" fn type_find_closure_drop(data: glib_ffi::gpointer) {
-    Box::<Box<Fn(&mut TypeFind) + Send + Sync + 'static>>::from_raw(data as *mut _);
+unsafe extern "C" fn type_find_closure_drop<F: Fn(&mut TypeFind) + Send + Sync + 'static>(
+    data: glib_ffi::gpointer,
+) {
+    Box::<F>::from_raw(data as *mut _);
 }
 
 unsafe extern "C" fn type_find_peek(data: glib_ffi::gpointer, offset: i64, size: u32) -> *const u8 {