Functions and Records

Closures

Capturing Outer State

A function declared inside another function can read and update names from the enclosing scope. The captured binding lives as long as the inner function does, so a factory can hand out a function that owns private mutable state.

Program

Play the program to build a counter closure and call it twice.

closures.dart 
int Function() makeCounter() {
  var count = 0;
  return () {
    count += 1;
    return count;
  };
}

void main() {
  var next = makeCounter();
  var a = next();
  var b = next();
  print('$a $b');
}
closure An inner function captures names from its enclosing scope.
captured mutation `count += 1` updates the same binding across calls; the closure carries the state.
factory function `int Function() makeCounter()` returns a fresh zero-argument function with its own private `count`.