Explain async, await in Flutter/Dart?

Asynchronous operations let your program complete work while waiting for another operation to finish. Here are some common asynchronous operations:

• Fetching data over a network.
• Writing to a database.
• Reading data from a file.

To perform asynchronous operations in Dart, you can use the Future class and the async and await keywords.

The async and await keywords provide a declarative way to define asynchronous functions and use their results. Remember these two basic guidelines when using async and await:

• To define an async function, add async before the function body
• The await keyword works only in async functions.

An async function runs synchronously until the first await keyword. This means that within an async function body, all synchronous code before the first await keyword executes immediately.

Consider an example:

import 'dart:async';

class Employee {
  int id;
  String firstName;
  String lastName;
  
  Employee(this.id, this.firstName, this.lastName);
}

void main() async {
  print("getting employee...");
  var x = await getEmployee(33);
  print("Got back ${x.firstName} ${x.lastName} with id# ${x.id}");
}

Future<Employee> getEmployee(int id) async {
  //Simluate what a real service call delay may look like by delaying 2 seconds   
  await Future<Employee>.delayed(const Duration(seconds: 2));
  //and then return an employee - lets pretend we grabbed this out of a database 
  var e = new Employee(id, "Joe", "Coder");
  return e;
}