Way to perfectly forward an argument. Need to improve this - c++

Question

Tried to make universal solution for my template function GenerateDictionary(...) to accept both rvalue and lvalue as generator.
This works, but I'm not sure that this is a correct way of making perfect forwarding here. I'll be happy to see any suggestions how to improve this example.
std::string GenerateWord(std::mt19937& generator, int max_length) {
const int length =
std::uniform_int_distribution(1, max_length)(generator);
std::string word;
word.reserve(length);
for (int i = 0; i < length; ++i) {
word.push_back(
std::uniform_int_distribution<int>('a', 'z')(generator));
}
return word;
}
template <template <typename> typename Container, typename Rand>
Container<std::string> GenerateDictionary(Rand&& generator, int word_count,
int max_length) {
std::vector<std::string> words;
words.reserve(word_count);
for (int i = 0; i < word_count; ++i) {
words.push_back(
GenerateWord(std::forward<Rand&>(generator), max_length));
}
return Container(words.begin(), words.end());
}
I understand that perfect forwarding may be pointless here, but anyway I want to know the safe way to use it here. Tried this to avoid the function to accept anything except mt19937.
template <typename T>
class CanReserve {
struct Small {
char c;
};
struct Large {
char arr[2];
};
template <typename C>
static Small test(decltype(&C::reserve));
template <typename C>
static Large test(...);
public:
enum { value = sizeof(test<T>()) == sizeof(Small) };
};
template <typename Rand,
typename = std::enable_if<std::is_same_v<Rand, std::mt19937>>>
std::string GenerateWord(Rand&& generator, int max_length) {
const int length =
std::uniform_int_distribution(1, max_length)(generator);
std::string word;
word.reserve(length);
auto letter_distr = std::uniform_int_distribution<int>('a', 'z');
for (int i = 0; i < length; ++i) {
word.push_back(letter_distr(generator));
}
return word;
}
template <template <typename...> typename Container, typename Rand,
typename = std::enable_if<std::is_same_v<Rand, std::mt19937>>>
Container<std::string> GenerateDictionary(Rand&& generator, int word_count,
int max_length) {
Container<std::string> words;
if constexpr (CanReserve<Container<std::string>>::value) {
words.reserve(word_count);
}
for (int i = 0; i < word_count; ++i) {
words.push_back(
GenerateWord(std::forward<Rand>(generator), max_length));
}
return words;
}