I'm having trouble with implementing a trait bound generic parameter for an entity that sends messages to a proper entity depending on the message. Imagine a trait called MessageTrait and MessageSender:

pub trait MessageTrait: Serialize + Clone + PartialEq {} // trait to allow concrete message (e.g. Message2) to be substituted in MessageSender

pub trait MessageSender {
    fn send_message(&mut self, message: &Message);
}

And messages message1..messageN (only Messag1 shown):

// messages to send
#[derive(Debug, Clone, Serialize, PartialEq)]
pub struct Message1 {}
impl MessageTrait for Message1 {}

And protocol specific MessageSender that sends MessageX using UDP:

// UDP send
pub struct UdpSender { // UpdSender fields }

impl MessageSender for UdpSender {
    fn send_message(&mut self, message: &Message1) {
        let send_msg = message.clone();
        // ... do stuff to send data using UDP
    }
}

// impl MessageSender for UdpSender { ... }

And finally, a HashMap containing the MessageSenders keyed by a String that can be used find the correct MessageSender:

// Message Router
struct MessageRouter {
    HashMap maps;
}

impl MessageRouter {
    pub fn send_msg(&mut self, id: &str) {
    // ...
        if let Some(sender) = maps.get(id) {  // find sender in map 
            sender.send_message(message)
    }
}

The code above compiles, but, I would like to change the MessageRouter to take a generic type so I can substitute something other than UdpSender (e.g. TCP/Unix Socket or Stub for testing):

struct MessageRouter {
    HashMap>, maps; // error
}

but the following gives me an error: expected a type, found a trait

impl MessageRouter where T: MessageSender { // error 
    pub fn new() -> Self {
        Self {
            maps: HashMap::new(),
        }
    }
    
    pub fn send_msg(&mut self, id: &str, msg: &T) {
        // ...
        if let Some(sender) = maps.get_mut(id) {        
            sender.send_message(msg);
        ..
        }
    }
}

Also tried MessageSender>, but this doesn't work either. How can I define T to be a type that implements MessageSender trait so it can be used as a type HashMap in MessageRouter? Thanks.