Boost::GIL bits8* to gray8_ptr_t without reinterpret_cast?

Trying to work by the design guidelines for GIL, I use bits__ for my channel data types. I often have external data I'm wrapping into GIL image views. However, even using the bits__ types for data pointers, I have to add in a reinterpret_cast befor开发者_StackOverflowe I can create my image views. Take the following code

int width = 3;
int height = 2;

boost::gil::bits8 data8[] = {0, 1, 100, 200, 50, 51};
boost::gil::bits8* pBits8 = data8;
boost::gil::gray8_ptr_t pGray8 = pBits8;

boost::gil::gray8_view_t v = interleaved_view(width, height, pGray8, width * sizeof(boost::gil::bits8));

Results in the error on line 6 "error C2440: 'initializing' : cannot convert from 'boost::gil::bits8 *' to 'boost::gil::gray8_ptr_t' 1> Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast"

Delving into the source code as much as I can, it appears these types really are unreleated. bits8 is just unsigned char, but gray8_ptr_t is a pointer to a struct pixel<bits8,gray_layout_t>. The only element of this struct is a single bits8, so a reinterpret_cast looks safe. It also works fine for the tests I've thrown at it.

However, I wrap external data into image views quite often, and having a reinterpret_cast in every place feels problematic. Is there a safer way of constructing a pixel pointer for use in GIL?

Current workaround:

template<class Dest, class Src>
Dest gil_safe_ptr_cast(Src src)
{
    // this cast is unsafe, use reinterpret_cast 
    BOOST_STATIC_ASSERT(false);
}
template<> boost::gil::gray8_ptr_t gil_safe_ptr_cast(boost::gil::bits8* pBits8)
{
    return reinterpret_cast<boost::gil::gray8_ptr_t>(pBits8);
}
boost::gil::bits8* pBits8 = data8;
boost::gil::gray8_ptr_t pGray8 = gil_safe_ptr_cast<boost::gil::gray8_ptr_t>(pBits8); // works
boost::gil::bits16* pBits16 = NULL;
boost::gil::gray8_ptr_t pGray82 = gil_safe_ptr_cast<boost::gil::gray8_ptr_t>(pBits16); // compile error as expected

---

To convert from bits8* to gray8_ptr_t, create a struct pixel and provide the bits8 to the constructor:

gray8_ptr_t convert_gray8_ptr_t(bits8* src) {
    return new struct pixel<bits8,gray_layout_t>(*src);
}

To convert back, use the struct's conversion operator:

bits8* convert_bits8(gray8_ptr_t src) {
    bits8* result = new bits8;
    *result = (bits8) *src;
    return result;
}

Of course both of these functions allocate memory and are probably unnecessary as functions (better as inline code).

---

template<class Dest, class Src>
Dest gil_safe_ptr_cast(Src src)
{
    // this cast is unsafe, use reinterpret_cast 
    BOOST_STATIC_ASSERT(false);
}
template<> boost::gil::gray8_ptr_t gil_safe_ptr_cast(boost::gil::bits8* pBits8)
{
    return reinterpret_cast<boost::gil::gray8_ptr_t>(pBits8);
}
boost::gil::bits8* pBits8 = data8;
boost::gil::gray8_ptr_t pGray8 = gil_safe_ptr_cast<boost::gil::gray8_ptr_t>(pBits8); // works
boost::gil::bits16* pBits16 = NULL;
boost::gil::gray8_ptr_t pGray82 = gil_safe_ptr_cast<boost::gil::gray8_ptr_t>(pBits16); // compile error as expected