New lint: suggest transforming [T, ...].into_iter().collect() to [T, ...].into() #9524
Description
What it does
These collection types implement From<[T; N]>: HashSet, BTreeSet, BinaryHeap, LinkedList, VecDeque (and Vec).
These collection types implement From<[(K, V); N]>: HashMap, BTreeMap.
Suppose you want to construct one of these collections from variables that you have at hand. Constructing Vec is covered by the vec![] macro, but for other collections users may tend to write (I did): myset: HashSet<i32> = [1, 2].into_iter().collect();, but more concise form is myset: HashSet<i32> = [1, 2].into().
All these From<[...]> implementations were stabilized in Rust 1.56 with the 2021 edition. Rust code migrated from previous editions may also contain the superseded pattern.
Optionally this lint could also suggest to transform HashSet::from_iterator([1, 2].into_iterator()) into HashSet::from([1, 2]). Alternatively, users can opt into from_iter_instead_of_collect and then get the original lint.
This lint can be also viewed as a variant of iter_cloned_collect, but for arrays rather than slices.
Lint Name
array_into_std_collections
Category
complexity
Advantage
- More concise and explicit expression of intent.
- Not sure if there can be performance and/or compile-time evaluation advantages?
Drawbacks
None known.
Example
let _: HashSet<i32> = [1, 2].into_iter().collect();
let _: BTreeSet<i32> = [1, 2].into_iter().collect();
let _: BinaryHeap<i32> = [1, 2].into_iter().collect();
let _: LinkedList<i32> = [1, 2].into_iter().collect();
let _: VecDeque<i32> = [1, 2].into_iter().collect();
let _: HashMap<&str, i32> = [("a", 1), ("b", 2)].into_iter().collect();
let _: BTreeMap<&str, i32> = [("a", 1), ("b", 2)].into_iter().collect();Could be written as:
let _: HashSet<i32> = [1, 2].into();
let _: BTreeSet<i32> = [1, 2].into();
let _: BinaryHeap<i32> = [1, 2].into();
let _: LinkedList<i32> = [1, 2].into();
let _: VecDeque<i32> = [1, 2].into();
let _: HashMap<&str, i32> = [("a", 1), ("b", 2)].into();
let _: BTreeMap<&str, i32> = [("a", 1), ("b", 2)].into();