Merge pull request #1983 from mrwatts88/patch-1

Update comments on iterator behavior in closure examples

Author: marioidival

src/fn/closures/closure_examples/iter_find.md

@@ -24,24 +24,27 @@ fn main() {
     let vec1 = vec![1, 2, 3];
     let vec2 = vec![4, 5, 6];
 
-    // `iter()` for vecs yields `&i32`.
+    // `vec1.iter()` yields `&i32`.
     let mut iter = vec1.iter();
-    // `into_iter()` for vecs yields `i32`.
+    // `vec2.into_iter()` yields `i32`.
     let mut into_iter = vec2.into_iter();
 
-    // `iter()` for vecs yields `&i32`, and we want to reference one of its
-    // items, so we have to destructure `&&i32` to `i32`
-    println!("Find 2 in vec1: {:?}", iter     .find(|&&x| x == 2));
-    // `into_iter()` for vecs yields `i32`, and we want to reference one of
-    // its items, so we have to destructure `&i32` to `i32`
-    println!("Find 2 in vec2: {:?}", into_iter.find(| &x| x == 2));
+    // `iter()` yields `&i32`, and `find` passes `&Item` to the predicate.
+    // Since `Item = &i32`, the closure argument has type `&&i32`,
+    // which we pattern-match to dereference down to `i32`.
+    println!("Find 2 in vec1: {:?}", iter.find(|&&x| x == 2));
+    
+    // `into_iter()` yields `i32`, and `find` passes `&Item` to the predicate.
+    // Since `Item = i32`, the closure argument has type `&i32`,
+    // which we pattern-match to dereference down to `i32`.
+    println!("Find 2 in vec2: {:?}", into_iter.find(|&x| x == 2));
 
     let array1 = [1, 2, 3];
     let array2 = [4, 5, 6];
 
-    // `iter()` for arrays yields `&&i32`
-    println!("Find 2 in array1: {:?}", array1.iter()     .find(|&&x| x == 2));
-    // `into_iter()` for arrays yields `&i32`
+    // `array1.iter()` yields `&i32`
+    println!("Find 2 in array1: {:?}", array1.iter().find(|&&x| x == 2));
+    // `array2.into_iter()` yields `i32`
     println!("Find 2 in array2: {:?}", array2.into_iter().find(|&x| x == 2));
 }
 ```
@@ -53,13 +56,13 @@ item, use `Iterator::position`.
 fn main() {
     let vec = vec![1, 9, 3, 3, 13, 2];
 
-    // `iter()` for vecs yields `&i32` and `position()` does not take a reference, so
-    // we have to destructure `&i32` to `i32`
+    // `position` passes the iterator’s `Item` by value to the predicate.
+    // `vec.iter()` yields `&i32`, so the predicate receives `&i32`,
+    // which we pattern-match to dereference to `i32`.
     let index_of_first_even_number = vec.iter().position(|&x| x % 2 == 0);
     assert_eq!(index_of_first_even_number, Some(5));
 
-    // `into_iter()` for vecs yields `i32` and `position()` does not take a reference, so
-    // we do not have to destructure
+    // `vec.into_iter()` yields `i32`, so the predicate receives `i32` directly.
     let index_of_first_negative_number = vec.into_iter().position(|x| x < 0);
     assert_eq!(index_of_first_negative_number, None);
 }