Higher-Order Functions - Dart Programming

A function can take another function as an argument and call it inside. The parameter type int Function(int) describes the expected callback shape, and a function variable can point at different compatible functions over time.

Program

Play the program to pass two different callbacks through the same transform function.

higher_order.dart

int transform(int x, int Function(int) f) {
  return f(x);
}

int square(int n) => n * n;
int negate(int n) => -n;

void main() {
  int Function(int) fn = square;
  var first = transform(4, fn);
  fn = negate;
  var second = transform(4, fn);
  print('$first $second');
}

function value `fn = square` and `fn = negate` store functions themselves; no call happens until `fn(...)` is used.

function-type parameter `int Function(int) f` declares a parameter whose value is a function from `int` to `int`.

callback `f(x)` inside `transform` runs whichever function was passed in.