Re: shared_ptr - implicit conversion to bool

From: David Abrahams (dave_at_[hidden])
Date: 2003-01-29 14:21:16

"wasekvesely <vaclav.vesely_at_[hidden]>" <vaclav.vesely_at_[hidden]> writes:

> Hi,
>
> I've found this in "shared_ptr.hpp":
>
> // implicit conversion to "bool"
> typedef T * (this_type::*unspecified_bool_type)() const;
>
> operator unspecified_bool_type() const // never throws
> { return px == 0? 0: &this_type::get; }
>
> Why this is better than:
>
> operator bool() const
> { return px != 0; }
>
> What more can I do with somethin like this?

It's not that you can do more; quite the opposite.

    int f(long);
    int x = f(shared_ptr<int>()); // error

With operator bool(), that (and many other abuses) would compile.

-- 
                       David Abrahams
   dave_at_[hidden] * http://www.boost-consulting.com
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