prefer_foreach

Use 'forEach' and a tear-off rather than a 'for' loop to apply a function to every element.

The analyzer produces this diagnostic when a for loop is used to operate on every member of a collection and the method forEach could be used instead.

The following code produces this diagnostic because a for loop is being used to invoke a single function for each key in m:

void f(Map<String, int> m) {
  for (final key in m.keys) {
    print(key);
  }
}

Replace the for loop with an invocation of forEach:

void f(Map<String, int> m) {
  m.keys.forEach(print);
}