How to typedef a generic function? - dart

Question

I have a generic static method that looks like this:
static build<K>() {
return (GenericClass<K> param) => MyClass<K>(param);
}
So far I have tried:
typedef F = MyClass<K> Function(GenericClass<K> param);
but it says that:
The return type '(GenericClass<K>) → MyClass<K>' isn't a '(GenericClass<dynamic>) → MyClass<dynamic>', as defined by the method 'build'.
and
typedef F = SimpleViewModel<K> Function<k>(Store<K> param);
Which says that:
The return type '(GenericClass<K>) → MyClass<K>' isn't a '<K>(GenericClass<K>) → MyClass<K>', as defined by the method 'build'.
MyClass looks like this:
class MyClass<T> {
final GenericClass<T> param;
MyClass(this.param);
static build<K>() {
return (GenericClass<K> param) => MyClass<K>(param);
}
}
So, what is a valid typedef for it?

Answer 1

There are two concepts of "generic" when it comes to a typedef. The typedef can be generic on a type, or the typedef can refer to a generic function (or both):
A typedef which is generic on T:
typedef F<T> = T Function(T);
Then in usage:
F first = (dynamic arg) => arg; // F means F<dynamic>
F<String> second = (String arg) => arg; // F<String> means both T must be String
A typedef which refers to a generic function on M:
typedef F = M Function<M>(M);
Then in usage:
F first = <M>(M arg) => arg; // The anonymous function is defined as generic
// F<String> -> Illegal, F has no generic argument
// F second = (String arg) => arg -> Illegal, the anonymous function is not generic
Or both:
typedef F<T> = M Function<M>(T,M);
And in usage:
F first = <M>(dynamic arg1, M arg2) => arg2; // F means F<dynamic> so the T must be dynamic
F<String second = <M>(String arg1, M arg2) => arg2; // The T must be String, the function must still be generic on the second arg and return type