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//! Marker traits that help ensure that iterators are implemented properly.

/// Marker that states that `Self` can be obtained from the reference `&'a T`.
pub trait Ref<'a, T> {
    /// Performs the conversion, showing that it is possible.
    fn convert(val: &'a T) -> Self;
}
impl<'a, T> Ref<'a, T> for &'a T {
    fn convert(val: &'a T) -> &'a T {
        val
    }
}
impl<'a, T: Copy> Ref<'a, T> for T {
    fn convert(val: &'a T) -> T {
        *val
    }
}
impl<'a, K, V> Ref<'a, (K, V)> for (&'a K, &'a V) {
    fn convert(val: &'a (K, V)) -> (&'a K, &'a V) {
        let (ref k, ref v) = *val;
        (k, v)
    }
}
impl<'a, K: Copy, V> Ref<'a, (K, V)> for (K, &'a V) {
    fn convert(val: &'a (K, V)) -> (K, &'a V) {
        let (k, ref v) = *val;
        (k, v)
    }
}

/// Marker that states that `Self` can be obtained from the reference `&'a mut T`.
pub trait RefMut<'a, T> {
    /// Performs the conversion, showing that it is possible.
    fn convert(val: &'a mut T) -> Self;
}
impl<'a, T> RefMut<'a, T> for &'a mut T {
    fn convert(val: &'a mut T) -> &'a mut T {
        val
    }
}
impl<'a, K, V> RefMut<'a, (K, V)> for (&'a K, &'a mut V) {
    fn convert(val: &'a mut (K, V)) -> (&'a K, &'a mut V) {
        let (ref key, ref mut val) = *val;
        (key, val)
    }
}
impl<'a, K: Copy, V> RefMut<'a, (K, V)> for (K, &'a mut V) {
    fn convert(val: &'a mut (K, V)) -> (K, &'a mut V) {
        (val.0, &mut val.1)
    }
}