以特定结构作为参数的特性实现

Question

I have a trait for readable and writable streams (like TcpStream ):

pub trait MyTraitPool<T: Read + Write> {
    fn acquire(&self, &String) -> T;
    fn free(&self, T);
}

I want to implement that trait with TcpStream as T , so I would like to write

struct MyPool;

impl<T> MyTraitPool<T> for MyPool
    where T: Read + Write {

    fn acquire(&self, addr: &String) -> T {
        TcpStream::connect(addr.as_str()).unwrap()
    }

    fn free(&self, con: T) {
        con.shutdown(Shutdown::Both);
    }
}

I get the error "expected type parameter, found struct std::net::TcpStream " in the acquire method. As for the free method, I know that shutdown is TcpStream -specific, but I would like to have an implementation specific for TcpStream s at that point and hence be able to call TcpStream -specific methods. So how do I go about doing so?

As a side note: the implementation is just an example for what kind of things I would like to do, not for how the code operates later!

Answer 1

Instead of making the MyTraitPool trait generic, you'd make your MyPool generic and you'd create an intermediate MyStream trait to offer you all methods you need:

trait MyStream: Read + Write {
    fn connect(&str) -> Self;
    fn shutdown(self);
}
impl MyStream for TcpStream {
    fn connect(addr: &str) -> Self { TcpStream::connect(addr) }
    fn shutdown(self) { TcpStream::shutdown(self, Shutdown::Both); }
}
impl<T: MyStream> MyTraitPool for MyPool<T> {
    fn acquire(&self, addr: &str) -> T {
        MyStream::connect(addr)
    }
    fn free(&self, con: T) {
        con.shutdown()
    }
}

Streams which do not actually need to shutdown, would simply leave the implementation empty.