cuda::proclaim_return_type

Defined in the header <cuda/functional>:

template <class Ret, class Fn>
__host__ __device__
unspecified<Ret, Fn> proclaim_return_type(Fn&& fn) {
  return unspecified<Ret, Fn>{fn};
}

cuda::proclaim_return_type creates a forwarding call wrapper that uses Ret as a return type. The wrapper is useful in the case of extended device lambdas since an attempt to determine the return type of their operator() function may work incorrectly in host code.

Template Parameters

Ret	Return type that’s being proclaimed
Fn	Callable object type that’s being wrapped

Parameters

fn	Callable object that’s being wrapped

Example

#include <cuda/functional>

template <class T, class Fn>
__global__ void example_kernel(T *out, Fn fn) {
  *out = fn();
}

__host__ void example() {
  auto fn = cuda::proclaim_return_type<char>([] __device__ () { return 'd'; });
  using rt = cuda::std::invoke_result_t<decltype(fn)>;

  rt* out {};
  cudaMalloc(&out, sizeof(rt));

  example_kernel<<<1, 1>>>(out, fn);

  // ...
}