Re: [Libxmlplusplus-general] Parser abstraction

[Christophe de Vienne <cdevienne alphacent com>]

Le Samedi 1 Février 2003 23:13, Stefan Seefeld a écrit :
> Christophe de Vienne wrote:
> >>again, would you derive your dom parser privately from the sax parser,
> >>i.e. would you use 'derived from' in terms of 'implemented by', I would
> >>(possibly) agree.
> >
> > Well, after rereading this long thread, I changed a little bit my mind on
> > the Parser abstraction, although I still have the feeling we should keep
> > it. If the two parsers doesn't have the same semantic as far as what they
> > produce, their parse_xxx methods do have exactly the same semantic, so
> > why not having them in a common interface, even if in 99.00% of cases
> > polymorphism will not be used.
>
> the dom parser's 'parse' method(s) returns a document, the sax parser's
> 'parse' method returns nothing. How's this semantically the same, or
> equivalent ?
>

I did not realise that in your exemple of create_document_from_file(...) the 
parse method returned something.
For me the parse methods tells the parser to do the actual parsing, after what 
we eventually go to get the result. Returning the Document would be the 
semantic of a createDocument method, which could cohexist with parse.
The two parsers, even if working very differently, has a common point : they 
parse something. I find logical to put the functions for that action in a 
common interface.

> (ok, I'm excluding the case where you have to assemble the document from
> chunks here)

This means that parse_file should return a Document while when using 
parse_chunk we would have to use an accessor to get it.
Is it really unbearable to write each time :
DomParser p;
p.parse(something);
Document * doc = p.getDocument();

especially if we introduce the create_document_from_file(...) function ?


>
> > Keeping it would permit, for exemple, to make an adaptator to be able to
> > parse from a new type of source which would be working for both parsers.
>
> I don't understand that. You are still talking about code reuse, right ?
>

no. The remark Jonathan Wakely about public inheritance made me realize that 
this is not the real interest of having a common interface.
The situation I was thinking of would be to create a class that is able to 
read a document from a special source, for exemple network with a weird 
protocol, and to which we could give the Parser which has to parse it.


My conclusion for now is that we would loose something (small but still) in 
removing the common interface, while I don't see what we gain.

I'd like to have some more points of view since we'll have to make a decision 
at last.


Best regards,

Christophe