Geesh, that was a silly and unnecessarily hard-to-find bug. The compiler was getting hung up on trying to infer the possible types of Transport trait implementations, as this determination is indeed circular. The issue with the compiler is not necessarily that it's unable to infer this, but that isn't giving a clearer error message, or a suggestion as to what to do

Author: Daniel Norman

src/network/mod.rs

@@ -15,7 +15,7 @@ struct NetworkInternals {
     next_slab_id: u32,
     slabs:     Vec<WeakSlab>,
     slab_refs: Vec<SlabRef>,
-    transports: Vec<Arc<Transport>>
+    transports: Vec<Arc<Transport + Send + Sync>>
 }
 
 pub struct NetworkShared {
@@ -47,7 +47,7 @@ impl Network {
 
         net
     }
-    pub fn add_transport (&self, transport: Arc<Transport> ) {
+    pub fn add_transport (&self, transport: Arc<Transport + Send + Sync> ) {
         let mut internals = self.shared.internals.lock().unwrap();
         internals.transports.push(transport);
     }

src/network/transport/transmitter.rs

@@ -8,7 +8,7 @@ pub trait DynamicDispatchTransmitter {
 }
 
 enum TransmitterInternal {
-    Local(), // TODO: How to use 
+    Local(), // TODO: How to use
     Simulator(SimulatorTransmitter),
     Dynamic(Box<DynamicDispatchTransmitter + Send + Sync>)
 }
@@ -19,8 +19,10 @@ pub struct Transmitter {
 
 impl Transmitter {
     /// Create a new transmitter associated with a local slab.
-    pub fn new_local(slab: &Slab) -> Self {
-        unimplemented!()
+    pub fn new_local(_slab: &Slab) -> Self {
+        Self {
+            internal: TransmitterInternal::Local()
+        }
     }
     /// Create a new transmitter associated with a local simulator transmitter.
     pub fn new_simulated(sim_tx: SimulatorTransmitter) -> Self {
@@ -44,7 +46,7 @@ impl Transmitter {
             Simulator(ref tx) => {
                 tx.send(from, memo);
             }
-            Dynamic(ref tx) => {
+            Dynamic(ref _tx) => {
                 unimplemented!()
             }
         }