How to minimize trait bounds repetition?

[culebron]

Question 1: here's some code I wrote, and it compiles, but I wonder if it's possible to write these trait bounds less times than I did? The compiler doesn't require them in type declaration, but on docs.rs every type with generics does have them. Should I keep them there?

pub trait IntoDuration {};
pub struct RawEdge {};

pub struct WeightedEdge<S: IntoDuration> {
    speed: S
}

impl<S: IntoDuration> WeightedEdge<S> {
    pub fn from_raw(de: &RawEdge) -> Self {
        todo!()
    }
}

pub struct Graph<S: IntoDuration> {
    edges: Vec<WeightedEdge<S>>,
}

impl<S: IntoDuration> Graph<S> {
    // take denorm edge, convert
    pub fn try_build<I>(&mut self, edges: I) -> Result<(), Box<dyn Error>> where I: Iterator<Item = RawEdge>, S: IntoDuration {
        todo!()
    }

}

Question 2: what to do if you need multiple traits and want to avoid repetition?

impl<'a, V: Copy + Hash + Eq, T: Clone> Iterator ...
//       ^^^^^^^^^^^^^^^^^^^
//       at least, maybe there's an alias for multiple traits?

[H2CO3]

Don't require bounds when they are not necessary. In the overwhelming majority of cases, they are not necessary on type declarations themselves. (The only exceptions I know of are when you want to use an associated type from a type parameter, or when you want to allow ?Sized.)

Your second question was answered yesterday.

[alice]

Another case where they are necessary on the type declaration is when you want to use methods from the trait in the Drop impl.