Re: [boost] xml?

Subject: Re: [boost] xml?
From: Stefan Seefeld (seefeld_at_[hidden])
Date: 2010-04-09 11:27:11

On 04/09/2010 11:14 AM, Larry Evans wrote:
> On 04/08/10 12:58, Stefan Seefeld wrote:
> [snip]
>
>> For the boost.xml library I'm working on I plan to use something akin 
>> to boost.variant as the return type of an xpath query. 
>
> What does boost.variant lack that leads you to create something
> akin to it?

Sorry, I'm not a native English speaker. By "akin to" I didn't mean to 
imply that it necessarily is something else. Just that boost.variant 
looks functionally like what I want, but that I haven't fully made up my 
mind about what the best interface is for this.

>
>> I don't think that the XPath specification should dictate a type 
>> hierarchy on a C++ implementation.
>>
>
> What is there about the XPath specification that makes any type
> hierarchy for modelling it less suitable than using something
> akin to boost.variant?

XPath queries may yield very different results, from mere integral 
numbers ("count(...)") to node-sets. I don't think it is meaningful or 
even possible to capture all those types in a single hierarchy (at least 
if by "hierarchy" we mean a common base class).

>
> You see, I'm wondering because using type hierarchies and
> virtual functions has been touted as a great advantage of
> OO programming; yet, it apparently lacks something which
> you need.

Indeed. Not everything can be captured with OO. Especially if you take 
that to the extreme of a single-rooted type hierarchy.

     Stefan

-- 
       ...ich hab' noch einen Koffer in Berlin...