Re: [boost] RFC: Boost.XML API prototype in the sandbox

From: Phil Endecott (spam_from_boost_dev_at_[hidden])
Date: 2007-07-11 14:23:25

David Abrahams wrote:
> on Fri Jul 06 2007, Stefan Seefeld <seefeld-AT-sympatico.ca> wrote:
>
>> over the last couple of years we have discussed possible XML APIs
>> for inclusion into boost. As I already had an early prototype for
>> such an API, I kept evolving it, based on feedback from those
>> discussions.
>> A couple of weeks ago I actually checked it into the sandbox
>> (http://svn.boost.org/trac/boost/browser/sandbox/xml). Today,
>> I adjusted the source layout to conform to the sandbox layout
>> we agreed on, including a boost.build - based build-system.
>>
>> I would appreciate if anybody interested into a future boost.xml
>> submission would have a look, provide feedback, or even get
>> involved into the (ongoing) development.
>
> Okay, this is going to sound very opinionated:
>
>   I find XML horrible to read

Agreed; I think it's just sufficiently good that a better alternative 
would fail.

>   however I find most of the procedural code I've seen for manipulating it even more horrible.

You've seen my code, haven't you :-)

> I would like to see a more declarative syntax for much of this stuff.

I prefer to read any constant fragments from files or from literal 
strings, which is about as declarative as you can get.

>     root.push_front(
>         tag("articleinfo")[
>              title ? (comment("This title was moved"), title) : NULL
>            , tag("author")[
>                  tag("firstname")["Joe"],
>                  tag("surname")["Random"]
>              ]
>         ]
>     )

How close can we get to that using Boost.Assign, if the element class 
is a model of a suitable container?

But I think that using subclasses is the key to making this sort of 
code easier on the eye:

struct firstname: public element {
   firstname(n): element("firstname",n) {};
};

etc.

articleinfo ai;
if (title) ai.push_back(comment("This title was moved"));
author a;
a.push_back(firstname("Joe"));
a.push_back(surname("Random"));
ai.push_back(a);
root.push_back(ai);

Just adding some non-standard indentation to that makes it almost as 
clear as I need.  You don't need the {}, but it keeps your editor's 
auto-indent happy:

articleinfo ai;
{
   if (title) ai.push_back(comment("This title was moved"));
   author a;
   {
     a.push_back(firstname("Joe"));
     a.push_back(surname("Random"));
     ai.push_back(a);
   }
   root.push_back(ai);
}

You can also reduce the declare-populate-add to delcare-populate if you 
pass the parent to the sub-elements' constructors:

articleinfo ai(root); {
   if (title) comment(ai,"This title was moved");
   author a(ai); {
     firstname(a,"Joe");
     surname(a,"Random");
   }
}

Of course there is a question of the lifespan of these 
apparently-temporary objects to resolve.  Anyway, I think that 
nice-looking XML-generating code can be possible without "resorting to" 
operator overloading.

Regards,

Phil.