Type Alias Message 

pub type Message = Box<dyn Any + Send>;

Any boxed type that may or may not contain data. They are fed to your applications update method to tell it how and what to update.

Typically, you will use the downcast_ref method on your messages to determine the type of the message, and extract the data from them if present.

Example

// the type of your message
struct HttpResponse(String);

// the boxed message itself
let http_response_message = Box::new(HttpResponse("Hello World".to_string()));

// determining the type of your message, and extracting the response
if let Some(res) = http_response_message.downcast_ref::<HttpResponse>() {
    // do something with the response
    // for example, setting it in the model to be rendered
    model.response = Some(res);
}

Aliased Type

pub struct Message(/* private fields */);