Two ways of comparing if two generics are of same type in Dart. There is a slight diff between these ways that may be important in some cases.

main.dart

/// Check whether two types are the same type in Dart when working with
/// generic types.
///
/// Uses the same definition as the language specification for when two
/// types are the same. Currently the same as mutual sub-typing.
bool sameTypes<S, V>() {
  void func<X extends S>() {}
  // Dart spec says this is only true if S and V are "the same type".
  return func is void Function<X extends V>();
}

bool equalTypes<S, V>() {
  return S == V;
}

class Nothing {}

class Something extends Nothing {}

void main() {
  //
  print(sameTypes<int, int>()); // true
  print(sameTypes<int, int?>()); // false
  print(equalTypes<int, int>()); // true
  print(equalTypes<int, int?>()); // false
  print('');
  //
  print(sameTypes<Nothing, Nothing>()); // true
  print(sameTypes<Nothing, Nothing?>()); // false
  print(equalTypes<Nothing, Nothing>()); // true
  print(equalTypes<Nothing, Nothing?>()); // false
  print('');
  //
  print(sameTypes<List<dynamic>, List<Object>>()); // false
  print(sameTypes<List<dynamic>, List<Object?>>()); // true
  print(equalTypes<List<dynamic>, List<Object>>()); // false 
  print(equalTypes<List<dynamic>, List<Object?>>()); // false
  print('');
  //
  print(sameTypes<Nothing, Something>()); // false
  print(sameTypes<Nothing?, Something?>()); // false
  print(equalTypes<Nothing, Something>()); // false
  print(equalTypes<Nothing?, Something?>()); // false
}