Flutter/Dart - Difference between () {} and () => {}

Question

In Flutter/Dart the examples sometimes show fat arrow and sometimes dont. Here are examples:

RaisedButton(
  onPressed: () {
    setState(() {
      _myTxt = \"         


        

Answer 1

=> Short hand expression is used to define a single expression in a function. Enough with the definition and properties.

• By using fat arrow => the curly brackets needs to be removed. Otherwise, the code editor will show you an error.
• If a function has a return type then by using a Fat arrow it is required to remove the return keyword.

Below Both are the same function and will return the same value. Just a different syntax

This is with => type

var size = (int s) => s*2;

This is return type

var size = (int s) { 
  return s*2; 
} 

To understand the concept with a real code example. We will consider the same examples that are done in Dart functions tutorial. The code executes the Perimeter and Area of a rectangle. This is how usually it is done with the help of functions.

 void main() {
  findPerimeter(9, 6);
  var rectArea = findArea(10, 6);
  print('The area is $rectArea');
}

void findPerimeter(int length, int breadth) {
  var perimeter = 2 * (length * breadth);
  print('The perimeter is $perimeter');
}

int findArea(int length, int breadth) {
  return length * breadth;
}

The given functions can be optimized with the help of fat arrow in Dart.

 void main() {
  findPerimeter(9, 6);
  var rectArea = findArea(10, 6);
  print('The area is $rectArea');
}

void findPerimeter(int length, int breadth) =>
  print('The perimeter is ${2 * (length * breadth)}');


int findArea(int length, int breadth) =>
   length * breadth;

After hitting the run button we are still getting the same result.

The perimeter is 108
The area is 60

Is from : https://flutterrdart.com/dart-fat-arrow-or-short-hand-syntax-tutorial/