Misleading Iterator::filter_map example

[dtolnay]

This is the example currently given for Iterator::filter_map:

let a = ["1", "2", "lol"];

let mut iter = a.iter().filter_map(|s| s.parse().ok());

assert_eq!(iter.next(), Some(1));
assert_eq!(iter.next(), Some(2));
assert_eq!(iter.next(), None);

I find it a bit misleading that there are 3 array elements and 3 asserts that do not correspond in the obvious way. It is too easy to skim this and interpret it as:

let a = ["1", "2", "lol"];

let mut iter = a.iter().map(|s| s.parse().ok());

assert_eq!(iter.next().unwrap(), Some(1));
assert_eq!(iter.next().unwrap(), Some(2));
assert_eq!(iter.next().unwrap(), None);

I think using ["1", "lol", "3", "NaN", "5"] with four asserts would avoid the confusion.

[dtolnay]

Ping @tshepang who last worked on this example. Would you be interested in making this change?

[tshepang]

will do