use std::borrow::Cow;

struct Foo<'a, T: 'a> where [T]: std::borrow::ToOwned {
    inner: Cow<'a, [T]>,
}

impl <'a, T>Foo<'a, T> where [T]: std::borrow::ToOwned {
    pub fn new<I: Into<Cow<'a, [T]>>>(inner: I) -> Self {
        Foo {
            inner: inner.into(),
        }
    }
}

fn main() {
    let a = "a".to_string();
    let b = "b".to_string();
    let c = "c".to_string();
    let d = "d".to_string();

    let exp = [a, b];
    let _a = Foo::new(&exp[..]);
    let _b = Foo::new(vec![c, d]);
}