You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: service.rs
    path of file: ./repos/ckb/util/types/src/core
    
    the code of the file until where you have to start completion: //! Types for CKB services.
//!
//! A CKB service acts as an actor, which pro
    
    pub fn call(sender: &Sender<Request<A, R>>, arguments: A) -> Option<R> {
        let (responder, response) = mpsc::channel();
        let _ = sender.send(Request {
            responder,
            arguments,
        });
        response.recv().ok()
    }