Hàm (Function) trong Dart

void sayHello() {
  print("Hello, Dart!");
}
 
sayHello();

void greet(String name) {
  print("Hello, $name!");
}
 
greet("Alice");

int sum(int a, int b) {
  return a + b;
}
 
var result = sum(10, 20);

int sum(int a, int b) => a + b;
 
void greet(String name) => print("Hello, $name!");

String greet(String name, [String? greeting]) {
  return "${greeting ?? 'Hello'}, $name!";
}
 
print(greet("Alice"));           // Hello, Alice!
print(greet("Bob", "Hi"));       // Hi, Bob!

void createUser({required String name, int age = 0}) {
  print("Name: $name, Age: $age");
}
 
createUser(name: "Alice");
createUser(name: "Bob", age: 25);

void greet({String name = "Guest", String greeting = "Hello"}) {
  print("$greeting, $name!");
}
 
greet();                    // Hello, Guest!
greet(name: "Alice");       // Hello, Alice!

void execute(Function callback) {
  callback();
}
 
execute(() => print("Callback executed"));

var list = [1, 2, 3];
 
list.forEach((item) {
  print(item);
});
 
// Arrow function
list.forEach((item) => print(item));