RE: [boost] operator bool() for smart pointers

From: Persson Jonas (jonas.persson_at_[hidden])
Date: 2002-05-08 04:31:40

> Adding an actual operator bool would have the bad side effect 
> of allowing you to use a smart pointer wherever an integer is 
> expected, and turning the pointer into the integer 1. You 
> lose quite a bit of type checking that way.
> 
> Some people have developed a "safe_bool" idiom where you 
> define a conversion to an obscure type of pointer (a 
> particularly obscure variant of a pointer to a member) so you 
> can do "if (p)" statements, but not "int i = p" statements. 
> It's used in the Boost function library.
> 
> We might want to consider using this technique in the smart 
> pointer library. It's inelegant in implementation, but a lot 
> of people like the "if (p)" idiom.
> 
>      -- Darin

Another possibility is to disable implicit conversion by
declaring another integer operator:

class X {
public:
 ...
  operator bool () { return px ; }
private:
  operator char ();
};

or am I missing some obvious drawback of this solution?

        / Jonas