pcg64 can't be printed

[ahh]

Here's an example that won't build for pcg_t = ::pcg64 but works for pcg_t = ::pcg32.

#include <random>
#include <sstream>

#include "third_party/pcg_random/include/pcg_random.hpp"

namespace {
  using pcg_t = ::pcg64;
}

int main()
{
  pcg_t rng(std::random_device{}());

  std::stringstream out;
  out << rng;

  return 0;
}

I can verify similar issues in pcg-test.cpp if you add prints to std::cout or reads from std::cin.

What I believe is happening is: you're relying on Koenig lookup to find the definitions of operator<< and operator>> in namespace pcg_extras. But pcg128_t is typically a typedef for __uint128_t; Koenig lookup doesn't work on typedefs (or more precisely, looks at the resolved type's namespace, not the typedef's.)

As I see it there are three possible fixes:

1. Move the operator definitions to the global namespace -- this is a bad idea, for one thing because anyone could have a conflicting definition.

2. Add a wrapper class around the typedef. This would solve the namespacing issue neatly; I don't know if we'd incur runtime cost from the compiler choking on the wrapper. Hopefully not but hard to prove.

3. Replace the operator<< for pcg128_t with similar free functions named (say) Input and Output and use SFINAE in the definitions of the engine operator<< to prefer those if available. A bit clunky, but would work. (Also sort of necessary for the uint8_t stuff, I think.)

I'm hacking together 3) to see how bad it looks, but not done yet.

[ahh]

Added #20 as an incomplete example of option 3).

[imneme]

I think this was fixed some time ago.