Clarification about type narrowing

[Scott Baden]

This line of code generated a compiler warning (below)

rput_strided<2>(&u[0][1], {sizeof(double),(cols+haloCol)*sizeof(double)}, ul, {sizeof(double), left_nbr_cols*sizeof(double)}, {1,(rows+haloRow)}, remote_cx::as_rpc([](int phase){
          nCount[phase]++;
          },phase) | operation_cx::as_promise(p) );

I'm not fond of shutting off casting around warnings unless I'm sure I'm OK I've also tried to perform the requisite type casting, but no go. Could I get some clarify please? The PG doesn't get into this level of detail. The code is in the upc++_optimized branch (belonging to Hadia) in the scott repo Hadia will give permission to those who don't already have it.

fillGhost-globalU-upcxx.cpp:49:47: error: non-constant-expression cannot be narrowed from type 'unsigned long' to 'std::__1::array<long, 2>::value_type' (aka 'long') in initializer list [-Wc++11-narrowing]
    rput_strided<2>(&u[0][1], {sizeof(double),(cols+haloCol)*sizeof(double)}, ul, {sizeof(double), left_nbr_cols*sizeof(double)}, {1,(rows+haloRow)}, remote_cx::as_rpc([](int phase){
                                                                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
fillGhost-globalU-upcxx.cpp:49:47: note: insert an explicit cast to silence this issue
    rput_strided<2>(&u[0][1], {sizeof(double),(cols+haloCol)*sizeof(double)}, ul, {sizeof(double), left_nbr_cols*sizeof(double)}, {1,(rows+haloRow)}, remote_cx::as_rpc([](int phase){
                                                                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                              static_cast<value_type>(     )

[Dan Bonachea]

Scott -

The problem is the stride arrays in the rput_strided overload you are using have element type ptrdiff_t:

  template<std::size_t Dim, typename T, /*goop*/>
/*goop*/
  rput_strided(
               T const *src_base,
               std::array<std::ptrdiff_t,Dim> const &src_strides,
               global_ptr<T> dest_base,
               std::array<std::ptrdiff_t,Dim> const &dest_strides,
               std::array<std::size_t,Dim> const &extents, /*goop*/);

sizeof(double) has type size_t (unsigned long), so you need to cast to ptrdiff_t (signed long) to match the element type in the function declaration.