Introduce MaybeSend trait in iced_futures

It allows to clean up all the `trait_aliases` modules!

futures/src/executor.rs

@@ -33,6 +33,7 @@ pub use self::smol::Smol;
 #[cfg(target_arch = "wasm32")]
 pub use wasm_bindgen::WasmBindgen;
 
+use crate::MaybeSend;
 use futures::Future;
 
 /// A type that can run futures.
@@ -43,12 +44,7 @@ pub trait Executor: Sized {
         Self: Sized;
 
     /// Spawns a future in the [`Executor`].
-    #[cfg(not(target_arch = "wasm32"))]
-    fn spawn(&self, future: impl Future<Output = ()> + Send + 'static);
-
-    /// Spawns a local future in the [`Executor`].
-    #[cfg(target_arch = "wasm32")]
-    fn spawn(&self, future: impl Future<Output = ()> + 'static);
+    fn spawn(&self, future: impl Future<Output = ()> + MaybeSend + 'static);
 
     /// Runs the given closure inside the [`Executor`].
     ///

futures/src/lib.rs

@@ -14,6 +14,7 @@
 pub use futures;
 
 mod command;
+mod maybe_send;
 mod runtime;
 
 pub mod executor;
@@ -35,6 +36,7 @@ pub mod time;
 
 pub use command::Command;
 pub use executor::Executor;
+pub use maybe_send::MaybeSend;
 pub use platform::*;
 pub use runtime::Runtime;
 pub use subscription::Subscription;

futures/src/maybe_send.rs

@@ -0,0 +1,21 @@
+#[cfg(not(target_arch = "wasm32"))]
+mod platform {
+    /// An extension trait that enforces `Send` only on native platforms.
+    ///
+    /// Useful to write cross-platform async code!
+    pub trait MaybeSend: Send {}
+
+    impl<T> MaybeSend for T where T: Send {}
+}
+
+#[cfg(target_arch = "wasm32")]
+mod platform {
+    /// An extension trait that enforces `Send` only on native platforms.
+    ///
+    /// Useful to write cross-platform async code!
+    pub trait MaybeSend {}
+
+    impl<T> MaybeSend for T {}
+}
+
+pub use platform::MaybeSend;

futures/src/runtime.rs

@@ -1,54 +1,10 @@
 //! Run commands and keep track of subscriptions.
-use crate::BoxFuture;
-use crate::{subscription, Executor, Subscription};
+use crate::subscription;
+use crate::{BoxFuture, Executor, MaybeSend, Subscription};
 
 use futures::{channel::mpsc, Sink};
 use std::marker::PhantomData;
 
-#[cfg(not(target_arch = "wasm32"))]
-mod trait_aliases {
-    use super::*;
-
-    pub trait RuntimeMessage: Send + 'static {}
-
-    impl<T> RuntimeMessage for T where T: Send + 'static {}
-
-    pub trait RuntimeMessageSender<Message: RuntimeMessage>:
-        Sink<Message, Error = mpsc::SendError> + Unpin + Send + Clone + 'static
-    {
-    }
-
-    impl<Message: RuntimeMessage, T> RuntimeMessageSender<Message> for T where
-        T: Sink<Message, Error = mpsc::SendError>
-            + Unpin
-            + Send
-            + Clone
-            + 'static
-    {
-    }
-}
-
-#[cfg(target_arch = "wasm32")]
-mod trait_aliases {
-    use super::*;
-
-    pub trait RuntimeMessage: 'static {}
-
-    impl<T> RuntimeMessage for T where T: 'static {}
-
-    pub trait RuntimeMessageSender<Message: RuntimeMessage>:
-        Sink<Message, Error = mpsc::SendError> + Unpin + Clone + 'static
-    {
-    }
-
-    impl<Message: RuntimeMessage, T> RuntimeMessageSender<Message> for T where
-        T: Sink<Message, Error = mpsc::SendError> + Unpin + Clone + 'static
-    {
-    }
-}
-
-pub use trait_aliases::{RuntimeMessage, RuntimeMessageSender};
-
 /// A batteries-included runtime of commands and subscriptions.
 ///
 /// If you have an [`Executor`], a [`Runtime`] can be leveraged to run any
@@ -67,8 +23,12 @@ where
     Hasher: std::hash::Hasher + Default,
     Event: Send + Clone + 'static,
     Executor: self::Executor,
-    Sender: RuntimeMessageSender<Message>,
-    Message: RuntimeMessage,
+    Sender: Sink<Message, Error = mpsc::SendError>
+        + Unpin
+        + MaybeSend
+        + Clone
+        + 'static,
+    Message: MaybeSend + 'static,
 {
     /// Creates a new empty [`Runtime`].
     ///

futures/src/subscription/tracker.rs

@@ -1,52 +1,8 @@
-use crate::{BoxFuture, Subscription};
+use crate::{BoxFuture, MaybeSend, Subscription};
 
 use futures::{channel::mpsc, sink::Sink};
 use std::{collections::HashMap, marker::PhantomData};
 
-#[cfg(not(target_arch = "wasm32"))]
-mod trait_aliases {
-    use super::*;
-
-    pub trait TrackerMessage: Send + 'static {}
-
-    impl<T> TrackerMessage for T where T: Send + 'static {}
-
-    pub trait TrackerMessageReceiver<Message: TrackerMessage>:
-        Sink<Message, Error = mpsc::SendError> + Unpin + Send + Clone + 'static
-    {
-    }
-
-    impl<Message: TrackerMessage, T> TrackerMessageReceiver<Message> for T where
-        T: Sink<Message, Error = mpsc::SendError>
-            + Unpin
-            + Send
-            + Clone
-            + 'static
-    {
-    }
-}
-
-#[cfg(target_arch = "wasm32")]
-mod trait_aliases {
-    use super::*;
-
-    pub trait TrackerMessage: 'static {}
-
-    impl<T> TrackerMessage for T where T: 'static {}
-
-    pub trait TrackerMessageReceiver<Message: TrackerMessage>:
-        Sink<Message, Error = mpsc::SendError> + Unpin + Clone + 'static
-    {
-    }
-
-    impl<Message: TrackerMessage, T> TrackerMessageReceiver<Message> for T where
-        T: Sink<Message, Error = mpsc::SendError> + Unpin + Clone + 'static
-    {
-    }
-}
-
-pub use trait_aliases::{TrackerMessage, TrackerMessageReceiver};
-
 /// A registry of subscription streams.
 ///
 /// If you have an application that continuously returns a [`Subscription`],
@@ -101,8 +57,12 @@ where
         receiver: Receiver,
     ) -> Vec<BoxFuture<()>>
     where
-        Message: TrackerMessage,
-        Receiver: TrackerMessageReceiver<Message>,
+        Message: 'static + MaybeSend,
+        Receiver: 'static
+            + Sink<Message, Error = mpsc::SendError>
+            + Unpin
+            + MaybeSend
+            + Clone,
     {
         use futures::{future::FutureExt, stream::StreamExt};
 

native/src/subscription.rs

@@ -3,41 +3,10 @@ use crate::event::{self, Event};
 use crate::Hasher;
 
 use iced_futures::futures::{self, Future, Stream};
-use iced_futures::BoxStream;
+use iced_futures::{BoxStream, MaybeSend};
 
 use std::hash::Hash;
 
-#[cfg(not(target_arch = "wasm32"))]
-mod trait_aliases {
-    use super::*;
-
-    /// Wrapper type
-    pub trait RunnerStream<Message>:
-        Stream<Item = Message> + Send + 'static
-    {
-    }
-
-    impl<T, Message> RunnerStream<Message> for T where
-        T: Stream<Item = Message> + Send + 'static
-    {
-    }
-}
-
-#[cfg(target_arch = "wasm32")]
-mod trait_aliases {
-    use super::*;
-
-    /// Wrapper type
-    pub trait RunnerStream<Message>: Stream<Item = Message> + 'static {}
-
-    impl<T, Message> RunnerStream<Message> for T where
-        T: Stream<Item = Message> + 'static
-    {
-    }
-}
-
-pub use trait_aliases::RunnerStream;
-
 /// A request to listen to external events.
 ///
 /// Besides performing async actions on demand with [`Command`], most
@@ -87,7 +56,7 @@ pub fn events_with<Message>(
     f: fn(Event, event::Status) -> Option<Message>,
 ) -> Subscription<Message>
 where
-    Message: 'static + Send,
+    Message: 'static + MaybeSend,
 {
     Subscription::from_recipe(Runner {
         id: f,
@@ -109,7 +78,7 @@ where
 pub fn run<I, S, Message>(id: I, stream: S) -> Subscription<Message>
 where
     I: Hash + 'static,
-    S: Stream<Item = Message> + Send + 'static,
+    S: Stream<Item = Message> + MaybeSend + 'static,
     Message: 'static,
 {
     Subscription::from_recipe(Runner {
@@ -190,13 +159,13 @@ where
 pub fn unfold<I, T, Fut, Message>(
     id: I,
     initial: T,
-    mut f: impl FnMut(T) -> Fut + Send + Sync + 'static,
+    mut f: impl FnMut(T) -> Fut + MaybeSend + Sync + 'static,
 ) -> Subscription<Message>
 where
     I: Hash + 'static,
-    T: Send + 'static,
-    Fut: Future<Output = (Option<Message>, T)> + Send + 'static,
-    Message: 'static + Send,
+    T: MaybeSend + 'static,
+    Fut: Future<Output = (Option<Message>, T)> + MaybeSend + 'static,
+    Message: 'static + MaybeSend,
 {
     use futures::future::{self, FutureExt};
     use futures::stream::StreamExt;
@@ -222,7 +191,7 @@ impl<I, S, F, Message> Recipe<Hasher, (Event, event::Status)>
 where
     I: Hash + 'static,
     F: FnOnce(EventStream) -> S,
-    S: RunnerStream<Message>,
+    S: Stream<Item = Message> + MaybeSend + 'static,
 {
     type Output = Message;
 
@@ -232,15 +201,6 @@ where
     }
 
     fn stream(self: Box<Self>, input: EventStream) -> BoxStream<Self::Output> {
-        use futures::stream::StreamExt;
-
-        #[cfg(target_arch = "wasm32")]
-        {
-            (self.spawn)(input).boxed_local()
-        }
-        #[cfg(not(target_arch = "wasm32"))]
-        {
-            (self.spawn)(input).boxed()
-        }
+        iced_futures::boxed_stream((self.spawn)(input))
     }
 }