Re: [boost] proto::or_ arity

From: Larry Evans (cppljevans_at_[hidden])
Date: 2007-04-19 05:37:53

On 04/19/2007 03:54 AM, Larry Evans wrote:
> On 04/18/2007 01:06 PM, Eric Niebler wrote:
> 
>>Larry Evans wrote:
> 
> [snip]
> 
>>>I've just encounted a need for something like this.  For example,
>>>if you have a list of types for which you want to apply the or_ to,
>>>however, that list must by calculated, then the only way to apply
>>>or to it is with a fold operation.  Since mpl::fold takes
>>>an argument represening the initial state, this would naturally
>>>be proto::or_<> in case you want to proto::or_ together a list
>>>of types.
>>
>><snip>
>>
>>Interesting. In order for this to work, proto::or_ would need to be an 
>>extensible mpl sequence, right? 
> 
> [snip]
> 
> No. The input to fold has to be; however, the output produced doesn't.
[snip]
I think the output could be adapted to conform to mpl sequence
requirements.  I've got a fold_seq template which does this, in case
you're interested.