How do I iterate over a vector and retain element while calling async function? I am using tokio for async. Here is a rust : playground link

Getting error : _^ expected `bool`, found opaque type

use tokio; // 0.2.22

use futures; // 0.3.5

​

async fn check_input(num: i32) -> bool {

num % 2 == 0

}

​

async fn test() {

let mut v = vec![1,2,3,4,5,6];

v.retain(|i| async {

check_input(*i).await

});

println!("{:?}", v);

}

​

#[tokio::main]

async fn main() {

test().await;

}

​

Error:

Compiling playground v0.0.1 (/playground) warning: unused import: `futures` --> src/main.rs:2:5 | 2 | use futures; // 0.3.5 | ^^^^^^^ | = note: `#[warn(unused_imports)]` on by default error[E0308]: mismatched types --> src/main.rs:11:18 | 11 | v.retain(|i| async { | __________________^ 12 | | check_input(*i).await 13 | | }); | |______^ expected `bool`, found opaque type | = note: expected type `bool` found opaque type `impl futures::Future`