+ /// **What it does:** Checks for useless borrowed references.
+ ///
+ /// **Why is this bad?** It is mostly useless and make the code look more
+ /// complex than it
+ /// actually is.
+ ///
+ /// **Known problems:** It seems that the `&ref` pattern is sometimes useful.
+ /// For instance in the following snippet:
+ /// ```rust,ignore
+ /// enum Animal {
+ /// Cat(u64),
+ /// Dog(u64),
+ /// }
+ ///
+ /// fn foo(a: &Animal, b: &Animal) {
+ /// match (a, b) {
+ /// (&Animal::Cat(v), k) | (k, &Animal::Cat(v)) => (), // lifetime mismatch error
+ /// (&Animal::Dog(ref c), &Animal::Dog(_)) => ()
+ /// }
+ /// }
+ /// ```
+ /// There is a lifetime mismatch error for `k` (indeed a and b have distinct
+ /// lifetime).
+ /// This can be fixed by using the `&ref` pattern.
+ /// However, the code can also be fixed by much cleaner ways
+ ///
+ /// **Example:**
+ /// ```rust
+ /// let mut v = Vec::<String>::new();
+ /// let _ = v.iter_mut().filter(|&ref a| a.is_empty());
+ /// ```
+ /// This closure takes a reference on something that has been matched as a
+ /// reference and
+ /// de-referenced.
+ /// As such, it could just be |a| a.is_empty()