rust - `use` statement necessary for trait not used directly in this source file: why? -

in code below, removing second line result in compilation error saying:

type `std::io::net::tcp::tcplistener` not implement method in scope named `listen` 

since directly using listener (even though std uses internally), why need specify it?

use std::io::{tcplistener, tcpstream}; use std::io::{acceptor, listener};  fn handle_client(mut stream: tcpstream) {     // ... }  fn main() {     let args = std::os::args();     println!("{}", args);      let listener = tcplistener::bind("127.0.0.1", 80).unwrap();      let mut acceptor = listener.listen().unwrap();      stream in acceptor.incoming() {         spawn(proc() {             handle_client(stream.unwrap());         });     } } 

it design decision of language require explicit use of traits implement methods. example in following code:

use my::a; use my::b;  mod {   pub trait {     fn foo(&self);   }    pub struct b;    impl b {     pub fn bar(&self) {       println!("called `bar`.");     }   }    impl b {     fn foo(&self) {       println!("called `foo`.");     }   } }  fn main() {   // requires "use my::b".   let b = b;   b.bar();    // requires "use my::a".   b.foo(); } 

i believe motivation heavily due fact there no seamless way support multiple traits same method name. there lot of work being done traits atm https://github.com/rust-lang/rfcs/blob/master/active/0024-traits.md.