[boost] Re: Optional, tie, and iterator_adaptor

From: Daniel Frey (daniel.frey_at_[hidden])
Date: 2003-08-31 07:09:24

Joel de Guzman wrote:
> Although I don't see this as problematic:
> 
>     optional<int> x;
>      if (x)  
>         foo(x);
> 
> Or perhaps:
> 
>     optional<int> x;
>      if (!!x)  
>         foo(x);
> 
> We already have an implicit conversion to safe_bool and an 
> operator ! anyway. Keep it. There's nothing wrong with it:
> 
>     operator unspecified-bool-type() const;
>     bool operator!() const;

IMHO, there is something terribly wrong here because now optional<T> has 
two interfaces. The interface of optional itself and the interface of T. 
If you think that optional<T> can be used like T (having the 
value-interface), you are immediately fooled by if(x) as it doesn't 
check T's value. A pointer-interface is much cleaner as it gives the 
user a hint that he is using a wrapper and in practice, I always prefer 
to be a little more explicit on these things (even at the cost of an 
occasional * here and there) than to have silent bugs.

Regards, Daniel

-- 
Daniel Frey
aixigo AG - financial training, research and technology
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