Trait appliance::HandledBy

pub trait HandledBy<H: ?Sized>: Message {
    fn handle_by(self, handler: &mut H) -> Self::Result;
}

A dual trait for Handler. For any type of messages M and any type of handlers H, if impl Handler<M> for H, then impl HandledBy<H> for M. I.e. we can either ask “which messages can be handled by this appliance” or “which appliances can handle this message”, and the answers to these questions are dual. The trait HandledBy answers the second question.

Normally one should always implement Handler<M>, unless for some reason it is impossible to do. The dual HandledBy impl is then provided automatically.

Generic methods, on the other hand, should use the trait constraint T: HandledBy<H>, since the set of types for which T: HandledBy<H> is strictly larger than those for which H: Handler<T>. An example where the client would need to implement HandledBy is if they want to add custom messages for a library-provided handler type.

Required methods

fn handle_by(self, handler: &mut H) -> Self::Result

Handle the given message with the provided handler.

The return type is wrapped in order to remove generic parameters from this function. The actual result value can be recovered with ResultWrapper::downcast if the type of the result is known.

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Implementors

impl<H, M: Message> HandledBy<H> for M where
    H: Handler<M>, 

fn handle_by(self, handler: &mut H) -> Self::Result

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