containers 0.9.13

pub enum Cow<'a, A: 'a + ?Sized + ToOwned> {
    Borrowed(&'a A),
    Owned(<A as ToOwned>::Owned),
}

pub trait ToOwned {
   type Error;
   type Owned: Borrow<Self>;
   fn to_owned(&self) -> Result<Self::Owned, Self::Error>;
}