Here's some generic code I wrote in Rust recently. I had two unrelated iterators/collections and I needed to flatten and sort them into a single buffer. st

Here's some generic code I wrote in Rust recently. I had two unrelated iterators/collections and I needed to flatten and sort them into a single buffer. struct Data { idx: usize // ... } struct Foo { stuff: Vec<Vec<Data>> } struct Bar { stuff: Vec<Data> } fn flatten_and_sort (foo:Foo, bar:Bar) -> Vec<Data> { let mut output = foo.stuff.into_iter() .flat_map(|v| v.into_iter()) .chain(bar.stuff.into_iter()) .collect::<Vec<_>>(); output.sort_by(|lhs, rhs| lhs.idx.cmp(&rhs.idx)); output } Now you could argue that this is just "generics for collections" but the way those iterator combinators are written make heavy use of generics/traits that aren't immediately applicable for collections. Those same combinator techniques can be applied to a whole host of other abstractions that allow for that kind of user code, but it's only possible if the type system empowers library authors to do it.