#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum Target {
    WasVec,
    WasNotVec
}

enum Decider {
    Yes,
    No
}

impl From<(Decider, u8)> for Target {
    fn from(_: (Decider, u8)) -> Target {
        Target::WasNotVec
    }
}

impl<T> From<(Decider, Vec<T>)> for Target
    where T:Into<Target>
{
    fn from(_: (Decider, Vec<T>)) -> Target {
        Target::WasVec
    }
}

impl<K,V> From< (Decider, Vec<(K, V)>)> for Target
    where K: Into<Target>,
          V: Into<Target> {
              fn from(_: (Decider, Vec<(K, V)>)) -> Target {
                  Target::WasNotVec
              }
          }

fn main()
{
    use Decider::*;

    let t:Target = (Yes, 2u8).into();
    println!("{:?}", t);

    let v:Vec<u8> = vec![1,2];
    let tv:Target = (No, v).into();
    println!("{:?}", tv);

    let w: Vec<(u8, u8)> = vec![(1,2), (3,4)];
    let tw: Target = (Yes, w).into();
    println!("{:?}", tw);
}