Why does this use of callable class now work? - dart

Question

I am trying to get callable classes to work in dart, but I have ran into a few issues. First thing I realized is that a normal function
myFunc() {
return 'myFunc';
}
Function.apply(myFunc,null);
is not working as a callable.
Then I realized that if I do
final myFunc = () => 'myFunc';
Function.apply(myFunc,null);
this works.
So now I am trying it out with classes
class Cars {
call(Map<Symbol,dynamic> args) {
return "ride";
}
const Cars();
}
final cars = Cars();
final jobs = {cars.hashCode :cars};
void main() {
int code = cars.hashCode;
print(Function.apply(jobs[code],null));
}
but in DartPad I get the following error
Uncaught exception:
NoSuchMethodError: method not found: 'call'
Receiver: Closure 'call$1' of Instance of 'Cars'
Arguments: []
are there some restrictions on the call method? Or how it works with Function.apply() that I am not finding in the docs?
Thanks.

Answer 1

Your first example works fine for me, but your program needs an entry point:
myFunc() {
return 'myFunc';
}
void main() {
print(Function.apply(myFunc, null));
}
In your class example, your call method requires a Map, but you're passing null. There is no call method with zero arguments, hence the method not found: 'call' error.
One way to fix it is by adding an empty Map to the parameter list in Function.apply:
class Cars {
call(Map<Symbol,dynamic> args) {
return "ride";
}
const Cars();
}
final cars = Cars();
final jobs = {cars.hashCode :cars};
void main() {
int code = cars.hashCode;
print(Function.apply(jobs[code], [Map<Symbol,dynamic>()]));
}
It's worth noting that you can call any method on a class with any number of arguments:
class Car {
go(int speed, int wheels) {
print('$speed mph, $wheels wheels');
}
}
void main() {
var car = Car();
Function.apply(car.go, [50, 4]);
}