contravariant argument types: wanna?

[Steven Schveighoffer]

On Thu, 24 Sep 2009 12:47:12 -0400, grauzone <none at example.net> wrote:

> Steven Schveighoffer wrote:
>> The solution we ended up using is that *all* streams defined the seek  
>> function, even if they didn't support seeking, and if you called it on  
>> such objects, they just throw an exception.
>
> So, if you want to see if an object supports seeking, you must call the  
> method + catch the exception? How is this better than a dynamic cast?

It makes the requirement for things that want to wrap streams less  
stringent.  For example, I can implement a Buffer that handles both  
seekable and non-seekable streams instead of 2 buffer types.

It also has less of a penalty for cases where you know the stream is  
seekable.

-Steve