Cannot call ping on Client

> rustc templated-traits.rs
templated-traits.rs:37:5: 37:19 error: type `Client<,ClientConfig>` does not implement any method in scope named `ping`
templated-traits.rs:37     client.ping();
                           ^~~~~~~~~~~~~~
error: aborting due to previous error

Client::new returns a Client

pub enum ClientConfig {
    TestingConfig,
    ProductionConfig
}

pub struct PingResponse;

pub trait ServiceInterface {
    fn ping(&self) -> PingResponse;
}

pub struct Client<'a, T> {
    some_dependency: &'a T
}

impl<'a, T> Client<'a, T> {
    pub fn new(inject_dependency: &'a T) -> Client<'a, T> {
        Client { some_dependency: inject_dependency }
    }
}

impl<'a, T> ServiceInterface for Client<'a, T> {
    fn ping(&self) -> PingResponse {
        PingResponse
    }
}

pub fn main() {
    let config = TestingConfig;
    let client = Client::new(&config);
    client.ping();
}

Client::new returns a Trait

impl<'a, T> Client<'a, T> {
    pub fn new(inject_dependency: &'a T) -> ~ServiceInterface {
        ~Client { some_dependency: inject_dependency } as ~ServiceInterface
    }
}

impl<'a, T> Client<'a, T> {
    pub fn new(inject_dependency: &'a T) -> ~ServiceInterface {
        ~Client { some_dependency: inject_dependency } as ~ServiceInterface
    }
}

Failed to find implementation

templated-traits.rs:24:9: 24:16 error: value may contain references; add `'static` bound
templated-traits.rs:24         ~Client { some_dependency: inject_dependency } as ~ServiceInterface
                               ^~~~~~~
templated-traits.rs:24:9: 24:16 error: cannot pack type `~Client<,T>`, which does not fulfill `Send`, as a trait bounded by Send
templated-traits.rs:24         ~Client { some_dependency: inject_dependency } as ~ServiceInterface
                               ^~~~~~~
error: aborting due to 2 previous errors

gistfile1.txt

Questions:

1) Why do I have to return a ~ServiceInterface?
2) Does this change with DST?
3) Why does it fail to compile?
4) Is this (return a trait rather than the client) reasonable? I figure it's a good idea for testing *.
5) What else am I doing wrong here?

* assume Client makes a network connection and I want consumers to be able to swap in a test implementation