Question

Suppose:

struct P {
    P(int v);
};

int v;
P p = 0; // allow
P q = v; // Fail at compile time

How can achieve that? any template trick?

I am trying to write allocator which has special pointer properties. unfortunately std implementation uses implicit conversion from int to NULL pointer:

{ return __n != 0 ? _M_impl.allocate(__n) : 0; }

my pointer implementation:
http://code.google.com/p/asadchev/source/browse/trunk/projects/boost/cuda/mapped_ptr.hpp

my allocator implementation:
http://code.google.com/p/asadchev/source/browse/trunk/projects/boost/cuda/allocator.hpp

I want to enforce explicit construction using raw pointer to avoid nasty problems.

Answer 1

You can do it but you won’t like it

struct P {
private:
    struct null_absorb;

public:
    P(null_absorb *v);
};

int v;
P p = 0; // allow
P q = v; // Fail at compile time

This will only allow null pointer constants. In other words, zero compile time values.