clarify exercise

[rust-101.git] / src / part10.rs

diff --git a/src/part10.rs b/src/part10.rs
index a28b61174f2b56a7674acc7cde312fabecd5fee7..2ba31f3904a850588532f2a821585f4a8dfecbcf 100644 (file)
--- a/src/part10.rs
+++ b/src/part10.rs
@@ -125,10 +125,12 @@ pub fn print_and_count(b: &BigInt) {
 // then looks for numbers larger than some threshold, and prints them.
 fn inc_print_threshold(v: &Vec<i32>, offset: i32, threshold: i32) {
     //@ `map` takes a closure that is applied to every element of the iterator. `filter` removes
 // then looks for numbers larger than some threshold, and prints them.
 fn inc_print_threshold(v: &Vec<i32>, offset: i32, threshold: i32) {
     //@ `map` takes a closure that is applied to every element of the iterator. `filter` removes

-    //@ elements from the iterator that do not pass the test given by the closure.  Since all these
-    //@ closures compile down to the pattern described above, there is actually no heap allocation
-    //@ going on here. This makes closures very efficient, and it makes optimization fairly
-    //@ trivial: The resulting code will look like you hand-rolled the loop in C.
+    //@ elements from the iterator that do not pass the test given by the closure.
+    //@ 
+    //@ Since all these closures compile down to the pattern described above, there is actually no
+    //@ heap allocation going on here. This makes closures very efficient, and it makes
+    //@ optimization fairly trivial: The resulting code will look like you hand-rolled the loop in
+    //@ C.

     for i in v.iter().map(|n| *n + offset).filter(|n| *n > threshold) {
         println!("{}", i);
     }
     for i in v.iter().map(|n| *n + offset).filter(|n| *n > threshold) {
         println!("{}", i);
     }


@@ -162,5 +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!
 
 // 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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