How to use iterator item type as struct type parameter

Question

I have the following code:

pub struct Tree<T> {
    root: Box<Node<T>>,
    elements: HashSet<T>,
}

impl<T> Tree<T> {
    pub fn new<I>(source: I) -> Option<Tree<T>>
    where
        I: std::iter::Iterator,
        <I as Iterator>::Item: Hash,
        <I as Iterator>::Item: Eq,
    {
    ...
    }

How do I propagate <I as Iterator>::Item type to T? In other words, how can I write code like this:

let tree = Tree::new("test".chars());

Julius Kreutz · Accepted Answer · 2021-10-06T19:46:10.880

You can set the Iterator type with Iterator<Item = T>. So your code would look like this

impl<T> Tree<T> {
    pub fn new<I>(source: I) -> Option<Tree<T>>
    where
        I: Iterator<Item = T>,
        T: Hash,
        T: Eq,
    {
        ...
    }
}

If you want your whole Tree to just be able to maintain types that implement the Hash and Eq trait. You should define that in the implementation.

impl<T> Tree<T>
where
    T: Hash,
    T: Eq,
{
    pub fn new<I>(source: I) -> Option<Tree<T>>
    where
        I: Iterator<Item = T>,
    {
        None
    }
}

That way you won't have to define it for every method.

[Edit]

Removed trait bounds from struct because of this

How to use iterator item type as struct type parameter

1 Answers1