Better example in "Iterator" slide

[djmitche]

Discussed in https://github.com/google/comprehensive-rust/discussions/1269

^{Originally posted by **njr0** September 27, 2023} I had a few questions/thoughts on this section. 1. You don't really explain what the `type Item` is, unless I missed it. 2. I wondered if you'd be able to replace the `Self::Item` with `u32`, but of course you can't. 3. The `take(5)` is obviously to prevent overflow, but I think it's more interesting without that. At least, I think you might suggest the instructor or student removes it. It doesn't take too long to run and the output is great: ``` Compiling playground v0.0.1 (/playground) Finished dev [unoptimized + debuginfo] target(s) in 0.60s Running `target/debug/playground` thread 'main' panicked at 'attempt to add with overflow', src/main.rs:10:24 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace fib(0): 1 fib(1): 1 fib(2): 2 fib(3): 3 fib(4): 5 fib(5): 8 fib(6): 13 fib(7): 21 fib(8): 34 fib(9): 55 fib(10): 89 fib(11): 144 fib(12): 233 fib(13): 377 fib(14): 610 fib(15): 987 fib(16): 1597 fib(17): 2584 fib(18): 4181 fib(19): 6765 fib(20): 10946 fib(21): 17711 fib(22): 28657 fib(23): 46368 fib(24): 75025 fib(25): 121393 fib(26): 196418 fib(27): 317811 fib(28): 514229 fib(29): 832040 fib(30): 1346269 fib(31): 2178309 fib(32): 3524578 fib(33): 5702887 fib(34): 9227465 fib(35): 14930352 fib(36): 24157817 fib(37): 39088169 fib(38): 63245986 fib(39): 102334155 fib(40): 165580141 fib(41): 267914296 fib(42): 433494437 fib(43): 701408733 fib(44): 1134903170 fib(45): 1836311903 ``` I did think, however, that while this is an interesting iterator, it's a slightly weird example, being "apparently" infinite but actually only only capable of producing 46 results before overflowing. Would it be better to handle the overflow and terminate iteration when you get past the capacity of an u32? (The implementation is slightly weird too, in the it overflows one sooner than it needs to. 1,134,903,170 + 1,836,311,903 is obviously less than 4 billion (2,971,215,073) and is already stored in `next`. It also feels like a slightly odd example in that `.next()` mutates the item in a pretty fundamental way. But maybe that's not usual? Not sure. It felt like a slightly weird example to me.

[djmitche]

I think this is a good example of an iterator that is not over a collection. Such an iterator typically will mutate itself in next (most iterators do). But, we have covered collections already, so perhaps we should make some "interesting" iterator over a Vec or something like that?

The overflow conversation is an interesting one, and sounds like a good # More to Explore section.