I agree with you that the C# example is far more readable.

One thing I like about Rust is that you can implement traits on standard library types. You can imagine implementing a "Where" trait on e.g Vec<T> (btw, you don't have to, since "filter" is already there) that would return an iterator that can be used by the next method in the call chain.

Unfortunately you can't "extend" standard library or built-in Python types like this.

In Rust your example would be:

   strings.filter(|s| s.starts_with("a")).map(|s| s.len()).sum::<u32>()