Stream operator<< for device_reference

[ccecka]

Implicit conversions are not considered during template argument deduction. Currently, stream output of a device_reference<A> where A is non-template (e.g. int, float, double, mystruct) functions as expected, but fails when A is a template (e.g. thrust::complex<float>, mytemplate<int>).

Example:

#include <thrust/device_vector.h>
#include <thrust/complex.h>
#include <iostream>

int main() {
  thrust::device_vector<double> a(5);
  std::cout << a[2] << std::endl;   // Outputs '0' as expected

  thrust::device_vector<thrust::complex<double> > b(5);
  std::cout << b[2] << std::endl;   // XXX: Fails to compile despite operator<< being defined for thrust::complex<T>
}

This patch simply uses static_cast to force the conversion and mirrors operator<< defined for device_ptr<T>.

[jaredhoberock]

Thanks Cris. I think adding this functionality is OK, but a couple questions:

1. Why an overload for basic_ostream and not just ostream?
2. Instead of device_reference, this function should probably be overloaded for thrust::reference. device_reference will pick it up as a descendant of reference.
3. is operator>> also required?

[ccecka]

1. ostream = basic_ostream<char, std::char_traits<char>> and wostream = basic_ostream<wchar_t, std::char_traits<wchar_t>>. User-defined char_traits are rumored to exist...
2. I agree. The same should be done for device_ptr => thrust::pointer.
3. Hadn't considered it. At the moment, op>> doesn't work for any thrust::device_reference<A> because operator A&() can't be implemented. I suppose an impl would be of the form

template <typename C, typename T, typename X>
std::basic_istream<C,T>& operator>>(std::basic_istream<C,T>& s, thrust::device_reference<X>& x) {
  typename thrust::device_reference<X>::value_type t;
  s >> t;
  x = t;
  return s;
}

I guess it's nice for symmetry with std::vector.

I'll make these changes tomorrow.

[jaredhoberock]

Thanks. If operator>> doesn't already work with device_reference, let's not try to make it work right now. Also, same for pointer.

[ccecka]

Stream output operators for thrust::pointer and thrust::reference with Doxygen stubs for thrust::device_ptr and thrust::device_reference.

[jaredhoberock]

Please don't eliminate the newlines at the end of these files -- on some platforms, it causes a warning if the last line is not empty.

[jaredhoberock]

Thanks Cris, I added some notes inline on your commit.

[ccecka]

Clean diff.

[jaredhoberock]

Thanks Cris, it looks good to me! I will test & merge your fixes tomorrow.

[jaredhoberock]

The tests pass, so I can merge this change.

However, these fixes need to go into branch 1.8.2. Unfortunately, I can't change the target of this pull request -- can you target thrust:1.8.2 instead of thrust:master?