Re: Re: "any" suggestions

From: Kevlin Henney (kevlin_at_[hidden])
Date: 2001-07-14 08:27:40

Peter Dimov writes
>From: "Kevlin Henney" <kevlin_at_[hidden]>
>> In message <003001c10c2c$7faf3e10$2101bf0a_at_[hidden]>, Corwin Joy
>> <cjoy_at_[hidden]> writes
>> >Proposal 1:  A second "any" class which I will call anyx (for "any"
>> >eXtractable).
>[...]
>> >...skip the obvious implementation with virtual functions etc...
>>
>> Actually, I don't think this is something that you can skip. What is the
>> "obvious" implementation? Output is trivial, [...]
>
>Not that trivial.
>
>struct X {};
>
>anyx a = X(); // error, no operator<< (std::ostream&, X const &);

Of course this won't compile, nor is it supposed to. X does not satisfy
the additional requirements that Corwin placed on the contents of anyx:
support for << and >>. I think you may have missed the following snippet
in Corwin's proposal:

>The disadvantage of course is that the held type must support istream
>and ostream operators for "anyx" to work.

Kevlin
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