`missing_iterator_fold`

What it does

Lints implementations of core::iter::Iterator that do not specialize the fold method.

Advantage

• Methods that consume the entire iterator (for_each, count, ...) rely on fold by default and would benefit from fold being specialized.
• Adaptor iterators might use fold (or related methods) for their own usage and would benefit as well.

Drawbacks

Specialize it may not be faster than the default behavior.

Example

struct Iter(u8);
impl Iterator for Iter {
    type Item = u8;
    fn next(&mut self) -> Option<Self::Item> {
        todo!()
    }
}

Could be written as:

struct Iter(u8);
impl Iterator for Iter {
    type Item = u8;
    fn next(&mut self) -> Option<Self::Item> {
        todo!()
    }
    fn fold<B, F>(self, init: B, f: F) -> B
    where
        F: FnMut(B, Self::Item) -> B
    {
        todo!()
    }
}