Add exercise 10.2 (#24)

diff --git a/src/part10.rs b/src/part10.rs
index 39270dee3137ded4c9fddd96caffcf4f6a59cf8c..dc73d87f8d10598c0cd3643c377abefe28109d9b 100644 (file)
--- a/src/part10.rs
+++ b/src/part10.rs
@@ -164,5 +164,13 @@ fn filter_vec_by_divisor(v: &Vec<i32>, divisor: i32) -> Vec<i32> {
 // those numbers that sit at odd positions? A function that checks whether a vector contains a
 // certain number? Whether all numbers are smaller than some threshold? Be creative!
 
+// **Exercise 10.2**: We started the journey in Part 02 with `SomethingOrNothing<T>`, and later
+// learned about `Option<T>` in Part 04. `Option<T>` also has a `map` function.
+// [Read its documentation here.](https://doc.rust-lang.org/stable/std/option/enum.Option.html#method.map)
+// Which functions in previous Parts can you rewrite to use `map` instead?
+// (Hint: read the source code of `map`, and see if the pattern appears in your own code)
+// (Bonus: [`test_invariant` in Part 05](part05.html#section-6) doesn't use `match`,
+// but can you still find a way to rewrite it with `map`?)
+
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 //@ [next](part11.html)