Use .extend(some_iter) over .extend(some_iter.collect()) #10762
Description
What it does
Extend::extend takes an IntoIterator. Since every Iterator is also an IntoIterator, you can extend from an iterator; collect() an iterator before extend() from it leads to extra memory allocations and extra copying, and is probably a mistake.
Lint Name
extend_collect
Category
suspicious, perf
Advantage
Fewer memory allocations and fewer copying.
Drawbacks
Maybe collect() actually leads to a performance boost because of, say, better cache behavior, and is actually intentional.
Example
let mut v = vec![0i32];
v.extend((1..10).collect::<Vec<_>>());Could be written as:
let mut v = vec![0i32];
v.extend(1..10);