RE: [boost] Boosting boost

From: Sebastien Marc (sebmarc_at_[hidden])
Date: 2001-10-17 16:37:20

Thanks for the clarification Steve. 
I guess i read the article too quickly. My fault. For
some reason, i skipped the assignment:
multiA = multiB; 
from the code and believed the convertion was from an
any containing a long into a const char *.

Thanks for your prototype too.

Fernando is right. I cannot expect a convertion to
const char* to work because of the memory allocation
issues, and thanks for William for the clarification.
lexical_cast<string> will just do what i want.

I suspect other people will be tempted to naively cast
an any containing a long into a const char* using
any_cast until they realize that is not possible.

Thanks for your responses.

Seb.

--- scleary_at_[hidden] wrote:
> > Yes steve, i understood that.
> > 
> > What is not clear to me is that an exception is
> > thrown. I would have expected the convertion, the
> > actual cast from any, containing 5, to const char
> *)
> > to work. 
> > 
> > To me, the resulting string s should contain "5"
> but
> > instead the exception is thown.
> 
> Oh.  Sorry, I misunderstood your question.
> 
> Take a look at the beginning of the "any" docs at
> Kevlin's three points
> under "Motivation".  "any" preserves type
> differences (i.e., does *not*
> provide automatic conversions).  Conversions like
> what you want are supplied
> by boost::lexical_cast.
> 
> There doesn't exist a class taking advantage of
> lexical_cast like you want
> (right now, anyway -- maybe you could submit one?). 
> Here's a simple
> prototype for one: (warning: untested code :)
> 
> class variant
> {
>   private:
>     std::string data;
>   public:
>     template <typename T>
>     variant(const T & other)
>     :data(boost::lexical_cast<std::string>(other)) {
> }
>     template <typename T>
>     variant & operator=(const T & other)
>     {
>       data =
> boost::lexical_cast<std::string>(other);
>       return *this;
>     }
>     // Possibly add "operator T()" ???
>     template <typename T>
>     T as()
>     { return boost::lexical_cast<T>(data); }
> };
> 
> variant any_value;
> any_value = 5;
> std::string s = any_value.as<std::string>();
> 
> 	-Steve
> 
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> 

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