Async Examples are broken on wasm32 backend

[AlisCode]

Hey there,

I tried to compile the Pokedex example with cargo build --target wasm32-unknown-unknown but it failed, saying that there was a problem with the types of my futures not being Send.

Basically, the From<A> implementation for Command<T> in iced_futures/src/command.rs is requiring - even on wasm32 targets - that the A generic (so, the future) be Send. That's fine for the native backend, but the iced-futures wasm-bindgen backend doesn't want its futures to be Send because it's storing them in an Rc<RefCell<..>>, thus making the example crash.

Fiddled around in the source code, managed to get the example to work on wasm32 backend after this diff :

diff --git a/futures/src/command.rs b/futures/src/command.rs
index d4f99b8..60e08b7 100644
--- a/futures/src/command.rs
+++ b/futures/src/command.rs
@@ -27,6 +27,7 @@ impl<T> Command<T> {
     /// Creates a [`Command`] that performs the action of the given future.
     ///
     /// [`Command`]: struct.Command.html
+    #[cfg(not(target_arch = "wasm32"))]
     pub fn perform<A>(
         future: impl Future<Output = T> + 'static + Send,
         f: impl Fn(T) -> A + 'static + Send,
@@ -36,6 +37,19 @@ impl<T> Command<T> {
         }
     }

+    /// Creates a [`Command`] that performs the action of the given future.
+    ///
+    /// [`Command`]: struct.Command.html
+    #[cfg(target_arch = "wasm32")]
+    pub fn perform<A>(
+        future: impl Future<Output = T> + 'static,
+        f: impl Fn(T) -> A + 'static + Send,
+    ) -> Command<A> {
+        Command {
+            futures: vec![Box::pin(future.map(f))],
+        }
+    }
+
     /// Applies a transformation to the result of a [`Command`].
     ///
     /// [`Command`]: struct.Command.html
@@ -85,6 +99,7 @@ impl<T> Command<T> {
     }
 }

+#[cfg(not(target_arch = "wasm32"))]
 impl<T, A> From<A> for Command<T>
 where
     A: Future<Output = T> + 'static + Send,
@@ -96,6 +111,19 @@ where
     }
 }

+#[cfg(target_arch = "wasm32")]
+impl<T, A> From<A> for Command<T>
+where
+    A: Future<Output = T> + 'static,
+{
+    fn from(future: A) -> Self {
+        Self {
+            futures: vec![future.boxed_local()],
+        }
+    }
+}
+
+
 impl<T> std::fmt::Debug for Command<T> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         f.debug_struct("Command").finish()

Granted, the implementation is a bit hacky 😄 do you have a better way in mind ? I can make a PR with whatever you feel applicable.

Cheers!