[boost] Re: Proposal for any_cast to references

From: Unai Uribarri Rodríguez (unaiur_at_[hidden])
Date: 2003-01-22 16:34:14

Douglas Gregor wrote:
> 
> That wouldn't change. The only difference is that the existing semantics 
> return a copy of the ValueType when the type is correct, and throws 
> bad_any_cast on failure. The signature is:
> 
> template<typename ValueType>
>   ValueType any_cast(const any & operand);
> 
> In many cases, it would be more useful to get an actual reference to the held 
> value, so the folllowing signature(s) would be preferred:
> 
> template<typename ValueType> ValueType& any_cast(any & operand);
> template<typename ValueType> const ValueType& any_cast(const any & operand);
> 
> If "operand" does not contain a value of type ValueType, any_cast throws 
> bad_any_cast. Otherwise, it returns a reference to the held value. Why 
> wouldn't we want this behavior?

I prefer to use any_cast<ValueType&>(x) to get a reference, since you 
state clearly your intention. Also, both static_cast and dynamic_cast 
uses that syntax.

I think that any_cast<ValueType>(x) shouldn't be equivalent to 
any_cast<ValueType&>(x), therefore any_cast<ValueType>(x) must have 
other semantics. It can return a copy or be illegal.