Initial trait-based workflow API skeleton

Author: Sushisource

workflow-api/src/lib.rs

@@ -80,7 +80,7 @@ impl<T> TemporalDeserializable for T {}
 mod tests {
     use super::*;
     use futures::FutureExt;
-    use std::collections::HashMap;
+    use std::{collections::HashMap, marker::PhantomData};
 
     // Workflow implementation example
     struct MyWorkflow {
@@ -112,6 +112,7 @@ mod tests {
         }
     }
 
+    // #[workflow] miiiight be necessary here, but, ideally is not.
     impl MyWorkflow {
         // Attrib commented out since nonexistent for now, but that's what it'd look like.
         // #[signal]
@@ -123,4 +124,37 @@ mod tests {
             self.bar.get(&arg).cloned()
         }
     }
+
+    // This would need to be moved into this crate and depended on by client
+    struct WorkflowHandle<WF: Workflow> {
+        _d: PhantomData<WF>,
+    }
+    struct SignalError; // just a placeholder
+    struct QueryError; // just a placeholder
+
+    // The signal/query macros would generate this trait and impl:
+    trait MyWorkflowClientExtension {
+        fn my_signal(&self, arg: String) -> BoxFuture<Result<(), SignalError>>;
+        fn my_query(&self, arg: String) -> BoxFuture<Result<Option<u64>, QueryError>>;
+    }
+    impl MyWorkflowClientExtension for WorkflowHandle<MyWorkflow> {
+        fn my_signal(&self, arg: String) -> BoxFuture<Result<(), SignalError>> {
+            // Is actually something like:
+            // self.signal("my_signal", arg.serialize())
+            todo!()
+        }
+
+        fn my_query(&self, arg: String) -> BoxFuture<Result<Option<u64>, QueryError>> {
+            todo!()
+        }
+    }
+
+    async fn client_example() {
+        // Now you can use the client like:
+        // (actually comes from client.start() or client.get_handle() etc)
+        let wfh = WorkflowHandle {
+            _d: PhantomData::<MyWorkflow>,
+        };
+        let _ = wfh.my_signal("hi!".to_string()).await;
+    }
 }