Proto for Boost mailing list page: Re: [proto] Thoughts on traversing proto expressions and reusing grammar

Subject: Re: [proto] Thoughts on traversing proto expressions and reusing grammar
From: Joel de Guzman (joel_at_[hidden])
Date: 2010-10-21 22:25:25

On 10/22/2010 8:53 AM, Eric Niebler wrote:
> On 10/21/2010 12:13 PM, Joel de Guzman wrote:
>>
>> Do you mean that it has to be exactly that to be called a "visitor"?
>> How exact? Does it have to be "an OO hierarchy with a virtual "Dispatch"
>> member that accepts a visitor"?
>
> No, there's some wiggle room. I tried to state in a latter message what
> I think the essence of the visitor design pattern is.
>
>> Does the Boost Variant visitation scheme (for example) satisfy these
>> conditions?
>
> The essentials are there, yeah. There is an implicit hierarchy, the root
> of which is, say, variant<A,B,C>. The subtypes are A, B and C. It's not
> a classic OO hierarchy, but admittedly that's not essential. There is a
> visitor. There are two dispatches: one on the "dynamic" type of the
> variant, either A, B, or C. There is second dispatch based on the type
> of the visitor. Pretty straightforward.
>
> Can you do a similar analysis for Thomas' code? I tried and am not
> certain about my results.

I am trying. I owe you guys some.

Regards,
-- 
Joel de Guzman
http://www.boostpro.com
http://spirit.sf.net