Update the type expected by View::operator[]

Signed-off-by: Andrea Bocci <andrea.bocci@cern.ch>

include/alpaka/mem/view/ViewAccessOps.hpp

@@ -22,6 +22,7 @@ namespace alpaka::internal
  using const_pointer = value_type const*;
  using reference = value_type&;
  using const_reference = value_type const&;
+ using Idx = alpaka::Idx<TView>;
 
  public:
  ViewAccessOps()
@@ -63,13 +64,13 @@ namespace alpaka::internal
  return data();
  }
 
- ALPAKA_FN_HOST auto operator[](std::size_t i) -> reference
+ ALPAKA_FN_HOST auto operator[](Idx i) -> reference
  {
  static_assert(Dim<TView>::value == 1, "operator[i] is only valid for Buffers and Views of dimension 1");
  return data()[i];
  }
 
- ALPAKA_FN_HOST auto operator[](std::size_t i) const -> const_reference
+ ALPAKA_FN_HOST auto operator[](Idx i) const -> const_reference
  {
  static_assert(Dim<TView>::value == 1, "operator[i] is only valid for Buffers and Views of dimension 1");
  return data()[i];
@@ -79,7 +80,6 @@ namespace alpaka::internal
  template<std::size_t TDim, typename TIdx>
  [[nodiscard]] ALPAKA_FN_HOST auto ptr_at([[maybe_unused]] Vec<DimInt<TDim>, TIdx> index) const -> const_pointer
  {
- using Idx = alpaka::Idx<TView>;
  static_assert(
  Dim<TView>::value == TDim,
  "the index type must have the same dimensionality as the Buffer or View");