From d9609db909acc0549dc72233178057da9c69b625 Mon Sep 17 00:00:00 2001 From: Matthew Watts Date: Sun, 4 Jan 2026 22:49:31 -0600 Subject: [PATCH] Update comments on iterator behavior in closure examples Clarify comments regarding iterator behavior for vecs and arrays. --- src/fn/closures/closure_examples/iter_find.md | 33 ++++++++++--------- 1 file changed, 18 insertions(+), 15 deletions(-) diff --git a/src/fn/closures/closure_examples/iter_find.md b/src/fn/closures/closure_examples/iter_find.md index e9803716cf..cbcc1ac542 100644 --- a/src/fn/closures/closure_examples/iter_find.md +++ b/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); }