Dart read-only function parameters.

main.dart

void main() {
  const two = 2;
  const ten = 10;
  var aNumber = ten;

  print('aNumber before pureAdd: $aNumber');
  print(pureAdd(aNumber, two));
  print('aNumber after pureAdd: $aNumber');

  print('aNumber before impureAdd: $aNumber');
  print(impureAdd(aNumber, two)); // why 102? something is wrong inside the impureAdd
  print('aNumber after impureAdd: $aNumber'); // but outside the function everything still fine
}

// Use the final modifier to make your parameters read-only inside function's scope
int pureAdd(final int a, final int b) {
//   a = 100; // uncomment this line and you will got an error
  return a + b;
}

int impureAdd(int a, int b) {
  a = 100; // oops!
  return a + b;
}