Re: nullptr placeholder without #define

Triple-DES <>
Fri, 6 Mar 2009 22:21:55 CST
On 6 Mar, 09:22, "" <>

I realy did not intend to simulate nullptr in such detail but it won't
hurt I suppose.

Current version looks like this:

const class nullptr_t {
     template<class T>
     operator T*() const { return 0; }
     template<class T, class U>
     operator T U::*() const { return 0; }

     void* p;

     void operator&() {}

} nullptr = nullptr_t();

nullptr should be constant (or more specifically it should be a literal)
and obtaining its address shouldn't be possible. I've also overloaded
operator!= ;).

Your nullptr still has a few semantical differences from the C++0x
equivalent per the latest draft:

if(nullptr); // implicit conversion to bool

Solution: operator bool() const { return false; }

nullptr_t(0); // conversion from integral null pointer
               // constant to nullptr_t

Solution: declare a private nested (incomplete) type Z, and a ctor
accepting a pointer to Z. Unfortunately, the class will no longer
support an initializer with braces, which nullptr_t does.

reinterpret_cast<int>(nullptr); // nullptr_t can be explicitly
                                 // converted to integral types

Solution: Seemingly impossible.

I think that's almost as close as you can get :)

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