rust - Error: not all control paths return a value [E0269] -

i newbie of rust. here code find indices of 2 numbers such add specific target.

use std::collections::hashmap;  fn two_sum(nums: &[i32], target: i32) -> [usize;2] {     let mut map: hashmap<i32, usize>  = hashmap::new();     in  0..nums.len() {         let want = target - nums[i];         match map.get(&nums[i]) {             some(&seen) => return [seen, i],             _ =>  map.insert(want, i),             };     }      [0usize, 0usize]; }  fn main() {     let nums = [1,3,7,4];     let res = two_sum(&nums, 10);     println! ("{},{}", res[0], res[1]); } 

i got error below

src/bin/2sum.rs:3:1: 15:2 error: not control paths return value [e0269] src/bin/2sum.rs:3 fn two_sum(nums: &[i32], target: i32) -> [usize;2] { src/bin/2sum.rs:4     let mut map: hashmap<i32, usize>  = hashmap::new(); src/bin/2sum.rs:5  src/bin/2sum.rs:6     in  0..nums.len() { src/bin/2sum.rs:7         let want = target - nums[i]; src/bin/2sum.rs:8         match map.get(&nums[i]) {               ... src/bin/2sum.rs:3:1: 15:2 help: run `rustc --explain e0269` see detailed     explanation error: aborting due previous error 

how happened there? how can solve problem?

thanks

you can remove semicolon after [0usize, 0usize] (this idiomatic) or add return [0usize, 0usize].

to improve code can return option. also, in case, better return tuple.

use std::collections::hashmap;  fn two_sum(nums: &[i32], target: i32) -> option<(usize, usize)> {     let mut map: hashmap<i32, usize> = hashmap::new();      in 0..nums.len() {         let want = target - nums[i];         match map.get(&nums[i]) {             some(&seen) => return some((seen, i)),             _ => map.insert(want, i),         };     }      none }  fn main() {     let nums = [1, 3, 7, 4];     let res = two_sum(&nums, 10);     println!("{:?}", res); }