Generically encapsulating random generators and distrubitons into a class template - performance

Question

I previously had a set of classes in one of my older libraries for working with the random number generators and distributions that was written when Visual Studio 2008 - 2010 were common place and before the release of 2012. I was starting a new project in Visual Studio 2017 so I decided to port my original version of the class over.
It was giving me a plethora of errors. So I had to modify the original class, and when I tried to make a generic function to use the above classes, I ended up facing some downfalls due to the fact that you can not partial specialize function templates. After enough frustrations for the past few days; I started over and rewrote the whole class. With the some of the newer features of C++11 & higher; I was able to use variadic templates which truly simplified things once I got use to the required syntax. So now that you have a bit of the history I can move on to my working example.
I have this class Generator that is working without errors to the best of my knowledge; it compiles, builds and runs without errors and I have tested a handful of different combinations of engines or generators, different seeding techniques with different distributions using their template type T.
#ifndef GENERATOR_H
#define GENERATOR_H
#include <limits>
#include <chrono>
#include <random>
#include <type_traits>
enum SeedType { USE_CHRONO_CLOCK, USE_RANDOM_DEVICE, USE_SEED_VALUE, USE_SEED_SEQ };
template<class Engine, class Type, template<typename> class Distribution>
class Generator {
public:
using Clock = std::conditional_t<std::chrono::high_resolution_clock::is_steady,
std::chrono::high_resolution_clock,
std::chrono::steady_clock>;
private:
Engine _engine;
Distribution<Type> _distribution;
Type _value;
public:
template<class... Params>
explicit Generator( Engine engine, Params... params ) : _engine( engine ) {
_distribution = Distribution<Type>( params... );
}
void seed( SeedType type = USE_RANDOM_DEVICE, std::size_t seedValue = 0, std::initializer_list<std::size_t> list = {} ) {
switch( type ) {
case USE_CHRONO_CLOCK: { _engine.seed( getTimeNow() ); break; }
case USE_RANDOM_DEVICE: { std::random_device device{};
_engine.seed( device() ); break; }
case USE_SEED_VALUE: { _engine.seed( seedValue ); break; }
case USE_SEED_SEQ: { std::seed_seq seq( list );
_engine.seed( seq ); break; }
}
}
void generate() { _value = _distribution( _engine ); }
Type getGeneratedValue() const { return _value; }
Distribution<Type> getDistribution() const { return _distribution; }
std::size_t getTimeNow() {
std::size_t now = static_cast<std::size_t>(Clock::now().time_since_epoch().count());
return now;
}
};
#endif // !GENERATOR_H
Using it is as simple as this demonstrating a few examples:
#include <iostream>
#include <iomanip>
#include <vector>
#include "generator.h"
int main() {
// Engine, Seeding Type, & Distribution Combo 1
std::mt19937 engine1;
Generator<std::mt19937, short, std::uniform_int_distribution> g1( engine1, 1, 100 );
g1.seed( USE_RANDOM_DEVICE );
std::vector<short> vals1;
for( unsigned int i = 0; i < 200; i++ ) {
g1.generate();
auto v = g1.getGeneratedValue();
vals1.push_back( v );
}
int i = 0;
for( auto& v : vals1 ) {
if( (i % 10) != 0 ) {
std::cout << std::setw( 3 ) << v << " ";
} else {
std::cout << '\n' << std::setw( 3 ) << v << " ";
}
i++;
}
std::cout << "\n\n";
// Engine, Seeding Type, & Distribution Combo 2
std::ranlux48 engine2;
std::initializer_list<std::size_t> list2{ 3, 7, 13, 17, 27, 31, 43 };
Generator<std::ranlux48, unsigned, std::binomial_distribution> g2( engine2, 50, 0.75 );
g2.seed( USE_SEED_SEQ, std::size_t(7), list2 );
std::vector<unsigned> vals2;
for( int i = 0; i < 200; i++ ) {
g2.generate();
auto v = g2.getGeneratedValue();
vals2.push_back( v );
}
i = 0;
for( auto& v : vals2 ) {
if( (i % 10) != 0 ) {
std::cout << std::setw( 3 ) << v << " ";
} else {
std::cout << '\n' << std::setw( 3 ) << v << " ";
}
i++;
}
std::cout << "\n\n";
// Engine, Seeding Type, & Distribution Combo 3
std::minstd_rand engine3;
Generator<std::minstd_rand, float, std::gamma_distribution> g3( engine3, 0.22222f, 0.7959753f );
g3.seed( USE_CHRONO_CLOCK );
std::vector<float> vals3;
for( int i = 0; i < 200; i++ ) {
g3.generate();
auto v = g3.getGeneratedValue();
vals3.push_back( v );
}
i = 0;
for( auto& v : vals3 ) {
if( (i % 5 ) != 0 ) {
std::cout << std::setw( 12 ) << v << " ";
} else {
std::cout << '\n' << std::setw( 12 ) << v << " ";
}
i++;
}
std::cout << "\n\n";
std::cout << "\nPress any key and enter to quit.\n";
std::cin.get();
return 0;
}
Is this an appropriate way to generically encapsulate the random generators & distributions? Are there any 'gotchas' that I'm missing? Finally, can this be improved for efficiency purposes? Or would it be more appropriate to ask this question on Code Review?