Draft first version of event subscriptions :tada:

3 files changed, 70 insertions, 1 deletions

diff --git a/core/Cargo.toml b/core/Cargo.toml
index c623ba78..0a8fd8ef 100644
--- a/core/Cargo.toml
+++ b/core/Cargo.toml
@@ -10,6 +10,8 @@ repository = "https://github.com/hecrj/iced"
 [features]
 # Exposes a future-based `Command` type
 command = ["futures"]
+# Exposes a future-based `Subscription` type
+subscription = ["futures"]
 
 [dependencies]
 futures = { version = "0.3", optional = true }
diff --git a/core/src/lib.rs b/core/src/lib.rs
index 65304e8b..6f13c310 100644
--- a/core/src/lib.rs
+++ b/core/src/lib.rs
@@ -9,7 +9,7 @@
 //! [Iced]: https://github.com/hecrj/iced
 //! [`iced_native`]: https://github.com/hecrj/iced/tree/master/native
 //! [`iced_web`]: https://github.com/hecrj/iced/tree/master/web
-#![deny(missing_docs)]
+//#![deny(missing_docs)]
 #![deny(missing_debug_implementations)]
 #![deny(unused_results)]
 #![deny(unsafe_code)]
@@ -38,3 +38,9 @@ mod command;
 
 #[cfg(feature = "command")]
 pub use command::Command;
+
+#[cfg(feature = "subscription")]
+pub mod subscription;
+
+#[cfg(feature = "subscription")]
+pub use subscription::Subscription;
diff --git a/core/src/subscription.rs b/core/src/subscription.rs
new file mode 100644
index 00000000..1e6695d6
--- /dev/null
+++ b/core/src/subscription.rs
@@ -0,0 +1,61 @@
+//! Generate events asynchronously for you application.
+
+/// An event subscription.
+pub struct Subscription<T> {
+    definitions: Vec<Box<dyn Definition<Message = T>>>,
+}
+
+impl<T> Subscription<T> {
+    pub fn none() -> Self {
+        Self {
+            definitions: Vec::new(),
+        }
+    }
+
+    pub fn batch(subscriptions: impl Iterator<Item = Subscription<T>>) -> Self {
+        Self {
+            definitions: subscriptions
+                .flat_map(|subscription| subscription.definitions)
+                .collect(),
+        }
+    }
+
+    pub fn definitions(self) -> Vec<Box<dyn Definition<Message = T>>> {
+        self.definitions
+    }
+}
+
+impl<T, A> From<A> for Subscription<T>
+where
+    A: Definition<Message = T> + 'static,
+{
+    fn from(definition: A) -> Self {
+        Self {
+            definitions: vec![Box::new(definition)],
+        }
+    }
+}
+
+/// The definition of an event subscription.
+pub trait Definition {
+    type Message;
+
+    fn id(&self) -> u64;
+
+    fn stream(
+        &self,
+    ) -> (
+        futures::stream::BoxStream<'static, Self::Message>,
+        Box<dyn Handle>,
+    );
+}
+
+pub trait Handle {
+    fn cancel(&mut self);
+}
+
+impl<T> std::fmt::Debug for Subscription<T> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("Command").finish()
+    }
+}