Unable to Understand this Flutter Closure Function Code? - flutter

Question

var callbacks = [];
for (var i = 0; i < 2; i++) {
callbacks.add(() => print(i));
}
callbacks.forEach((c) => c());
I dont Understand Two Things :
print(i) is of return-type Void, shouldnt the compiler show "error", because the work of print(i) is to print the item to the console and not return something.
in the line " callbacks.forEach((c) => c()); " how come c() became a function, because it was a parameter inside the lambda function to get values.
the link of the Code :
https://dart.dev/guides/language/language-tour#type-test-operators
under for Loops
PS : I am a beginner to this syntax, so Thank you so much for your Help Guys !

Answer 1

var callbacks = [];
for (var i = 0; i < 2; i++) {
callbacks.add(() => print(i));
}
callbacks.forEach((c) => c());
Here, () => print(i) is a closure which takes no arguments and returns void. In the loop, you add these functions to the callback list.
(c) => c() is a closure which takes a dynamic parameter and attempts to call it (i.e. calls c.call()).
Some type safety might be helpful here, for example:
final callbacks = <void Function()>[]; // an empty list of functions that look like () -> void
for (var i = 0; i < 2; i++) {
final void Function() callback = () => print(i);
callbacks.add(callback);
}
callbacks.forEach((void Function() callback) => callback());
In this example, because callbacks has a type of List<void Function()>, the parameter of the function passed to forEach is a void Function(), which means you can call it with c()