dart_functions.dart

dart_functions.dart

//import 'package:meta/meta.dart';
  
String f1() => 'value'; // For functions that contain just one expression, you can use a shorthand syntax

String f2() {  // this function equivalent to f1
  return 'value';
}

/// Functions as first-class objects
/// You can pass a function as a parameter to another function. For example and return function
void f3(Function f) {
  f(); 
}

/// Fluction return function
Function f4() {
  return f2;
}

// A function can have two types of parameters: required and optional. The required parameters are listed first, followed by any optional parameters. Optional parameters can be named or positional.
  
/// a1 - positional required
/// a2 - named optional
int f5(int a1, {int a2 = 6}) {
  return a1 + a2;
}

/// a1 - positional required
/// a2 - named required
int f6(int a1, {/*@required*/ int a2 = 6}) {
  return a1 + a2;
}
  
/// a1 - positional required
/// a2 - positional optional
int f7(int a1, [int a2 = 6]) {
  return a1 + a2;
}

// define function type
typedef Operation = int Function(int a, int b); 

int sum(int a, int b) => a + b;

int operation(int a, int b, {Operation op = sum}) {
  return op(a, b); // execute function
}

void main() { // entry point
  final func = operation; // function variable
  final result = func(1, 2, op: (int a, int b) => a * b); // op - anonymous function
  print(result);
  
}