async/.await

Additional Resources

• Starter guide to writing async Rust
• Crust of Rust: async/await

Exercises

Awaiting

// When executing the below code nothing is printed to console. Can you guess what is missing?

#[tokio::main]
async fn main() {
    my_function();
}

async fn my_function() {
    println!("My first asynchronous function in rust!");
}

#[tokio::main]
async fn main() {
  my_function().await;
}

async fn my_function() {
  println!("My first asynchronous function in rust!");
}

Creating executor

// Fix the code to make it compile. You may only add code, not remove it.

use std::time::Duration;
use tokio::time::sleep;

struct Employee {
    id: u32,
    name: String,
    salary: f32,
}

impl Employee {
    fn new(id: u32, name: &str, salary: f32) -> Self {
        Self {
            id,
            name: name.to_string(),
            salary,
        }
    }
}

fn main() {
    let (id1, id2) = (2, 3);
    let emp1 = read_details_from_db(id1).await.unwrap();
    let emp2 = read_details_from_db(id2).await.unwrap();
    if emp1.salary > emp2.salary {
        println!(
            "{} earns ${} more than {}",
            emp1.name,
            emp1.salary - emp2.salary,
            emp2.name
        );
    } else if emp2.salary > emp1.salary {
        println!(
            "{} earns ${} more than {}",
            emp2.name,
            emp2.salary - emp1.salary,
            emp1.name
        );
    } else {
        println!("Both {} and {} earn same amount", emp1.name, emp2.name);
    }
}

async fn read_details_from_db(id: u32) -> Result<Employee, String> {
    // dummy read from database
    sleep(Duration::from_millis(1000)).await;
    let database = [
        Employee::new(1, "Alice", 98000.0),
        Employee::new(2, "Bob", 95000.0),
        Employee::new(3, "Cindy", 95000.0),
    ];
    for emp in database {
        if id == emp.id {
            return Ok(emp);
        }
    }
    Err("Employee record not present".into())
}

use std::time::Duration;
use tokio::time::sleep;

struct Employee {
  id: u32,
  name: String,
  salary: f32,
}

impl Employee {
  fn new(id: u32, name: &str, salary: f32) -> Self {
      Self {
          id,
          name: name.to_string(),
          salary,
      }
  }
}

#[tokio::main]
async fn main() {
  let (id1, id2) = (2, 3);
  let emp1 = read_details_from_db(id1).await.unwrap();
  let emp2 = read_details_from_db(id2).await.unwrap();
  if emp1.salary > emp2.salary {
      println!(
          "{} earns ${} more than {}",
          emp1.name,
          emp1.salary - emp2.salary,
          emp2.name
      );
  } else if emp2.salary > emp1.salary {
      println!(
          "{} earns ${} more than {}",
          emp2.name,
          emp2.salary - emp1.salary,
          emp1.name
      );
  } else {
      println!("Both {} and {} earn same amount", emp1.name, emp2.name);
  }
}

async fn read_details_from_db(id: u32) -> Result<Employee, String> {
  // dummy read from database
  sleep(Duration::from_millis(1000)).await;
  let database = [
      Employee::new(1, "Alice", 98000.0),
      Employee::new(2, "Bob", 95000.0),
      Employee::new(3, "Cindy", 95000.0),
  ];
  for emp in database {
      if id == emp.id {
          return Ok(emp);
      }
  }
  Err("Employee record not present".into())
}