Dart in Functions

Anonymous functions

Programming for All

calc(int b) {
  int c = 1;

  return () => print("The value is ${b + c++}");
}

void main() {
  (a, b) {
    print("Hello, from Anonymous: ${a + b}");
  }(10, 20);

  var f = calc(2);
  f();
  calc(10)();
  f();
}

Class in Dart

We can use class in dart like this.

class Greeter {
  var greeting;
  var _dragon;

  sayKnight() {
    return "$greeting ${this.dragon}";
  }

  get dragon => _dragon;
  set dragon(value) => _dragon = value; 
}

main() {
  var greeter = new Greeter();
  greeter.greeting = "U must win";
  greeter.dragon = "General Nagar";
  print(greeter.sayKnight());
}

class Welcomer {
  printGreeting() => print("Hello ${dragon}");
  var dragon;
}
class Greeter implements Welcomer {
  printGreeting () => print("Greetings ${dragon}");
  var dragon;
}
void sayKnight(Welcome welcomer) {
  welcomer.printGreeting();
}

//Main functions

main() {
  var welcomer = new Welcomer();
  welcomer.name = "General Dragon";
  sayKnight(welcomer);

  var greeter = new Greeter();
  greeter.name = "General Dragon Knight";
  sayKnight(greeter);
  
}

Closure in Dart

calc(int b) {
  int c = 1;

  return () => print("The Value is ${ b + c++}");
}

void main() {
  var x = (a, b) {
    print("Hello, from Closure: {a + b}");
  };
}

//Declare function using function shorthand.

Single line function

String sayHello(name) => "Hello $name";

This is only use for Comments //

main() {
  var myFunc = sayHello; //Assign function in variable
  print(myFunc("World")); //Invoke function stored in var
//Define Anonymous function
  var mySumFunc = (a, b) {
    return a+b;
  };
  //Invoke or Call Anonymous function
  var c = mySumFunc(1, 2);  
  print(c);
}

Function

int add(int x, int y) => x + y;
int sub(int x, int y) => x - y;

choose(bool op) {
  if (op == true) {
    return add;
  } else {
    return sub;
  }
}

void main() {
  var result = choose(true);
  print("Resuly is ${result(40, 50)}");
}

HTML in Dart

For using html in dart programming. We must import first to use in flutter.

import ‘dart:html’;

import 'dart:html';

void main() {
  var button = new Element.tag("button");

  button.text = "Click me";
  button.onClick.map((event) {
    List buttonList = querySelectorAll("button");
    window.alert("There is ${buttonList.length} button");
  });
  document.body.children.add(button);
}

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