Regression boost 1.87: offset_ptr conversion from `void` no longer works

[liss-h]

Hello,

in boost <=1.86 the following always worked to convert a offset_ptr<void> to another type (e.g. offset_ptr<int>).

boost::interprocess::offset_ptr<void> x{};
auto y = boost::interprocess::offset_ptr<int>{x};

But since 1.87 it no longer works (the constraints are no longer satisfied) see: https://godbolt.org/z/T36xrvMnn

reinterpret_pointer_cast<int>(x) also does not work by default because it cannot infer the additional template params (difference type and such), so they would always need to be provided. I assume this is not intended.

If it is intended, I would be glad if you would show me the intended way for the conversion.

[igaztanaga]

Conversion from "void" to another type was an unsafe loophole, just like you can't convert a "void " to "int". But the xxx_cast functions are not working at all (bug) and they are not tested. You should be able to use reinterpret_pointer_cast<int>(x) or static_pointer_cast<int>(x). I'll commit a fix ASAP.

As a workaround, you can obtain the raw pointer using x.get(), do the static_cast<int*>(x.get()) and convert the raw int * pointer again to a offset_ptr<int>.