CODEWITHSUNDEEP
rust
yjlee
yjlee

Reputation: 553

For vector values, which is faster, for loop or for_each?

I'm trying to insert each item in a vector into a map. Which one is preferred and faster, using a for-loop or an iterator via for_each?

Upvotes: 3

Views: 2715

Answers (2)

Blubber
Blubber

Reputation: 1483

Interestingly, the documentation for the for_each method mentions that it can be faster than a normal for

This is equivalent to using a for loop on the iterator, although break and continue are not possible from a closure. It’s generally more idiomatic to use a for loop, but for_each may be more legible when processing items at the end of longer iterator chains. In some cases for_each may also be faster than a loop, because it will use internal iteration on adapters like Chain.

Source here

Upvotes: 1

René
René

Reputation: 408

The official documentation states that for and for_each have the same runtime performance:

"The implementations of closures and iterators are such that runtime performance is not affected. This is part of Rust’s goal to strive to provide zero-cost abstractions."

~ https://doc.rust-lang.org/book/ch13-04-performance.html

If you are unsure which of two different implementations is faster (no matter if its about for loops or not) you can always measure it yourself. When doing so make sure to use big arrays (maybe with a size of >100k) so that your measurements will be more accurate.

use std::time::{Instant};
use std::thread;
use std::time::Duration;

fn my_fun() {
    // Put your code here
}

fn main() {
    let current = Instant::now();
    
    my_fun();
    
    let duration = current.elapsed();
    
    println!("Time elapsed in MyFun() is: {:?}", duration);
}

Run this program with your implementations.

Upvotes: 6

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