Re: dynamic_cast is ugly!

From:
"Daniel T." <daniel_t@earthlink.net>
Newsgroups:
comp.lang.c++
Date:
Fri, 7 Mar 2008 13:50:08 -0800 (PST)
Message-ID:
<a5ffca7b-6862-4b6c-9f87-b29d81e011b9@n77g2000hse.googlegroups.com>
On Mar 7, 3:40 pm, Ian Collins <ian-n...@hotmail.com> wrote:

Daniel T. wrote:

On Mar 7, 2:58 pm, Ian Collins <ian-n...@hotmail.com> wrote:

Daniel T. wrote:

Because I program using OO idioms, not representational ones. Or to pu=

t

it another way, I specifically design my programs such that I don't ne=

ed

to use dynamic_cast... even occasionally.

There are occasions when the interface forces your hand. For example=

when implementing the W3C Document Object Model, where all of the
container types are collections of the the base object (Node). Node =

is

seldom used, most containers end up storing derived objects (Elements o=

r

Attributes) that extend the functionality of Node.


All I can say to that is that I have never had my hand forced. :-) The
question with the above is, do you know statically (i.e., at compile
time) the types of the objects? Even with generic containers like you
mention, if you only put in objects of type X, then you know that all
objects in the container are of type X.


No, that's the nasty bit.

Say you have an element type with an attribute you want to use (the link
in an XHTML anchor element for instance) and you wish to process all of
these elements in a document. The DOM interface provides a means of
extracting a list of them by name, but that list is a list of Nodes and
Node doesn't even have attributes!

I prefer to be able to write something like

dom::NodeList anchors(document.getElementsByTagName("A"));

html::Anchor a(anchors[n]);

and let the library do the conversion from Node to Anchor under the
hood. One benefit of using dynamic_cast is the conversion will fail if
the Node isn't the expected type.


I will be happy to grant that if you are coding in a representational
style instead of Object Oriented, you may very well have to use
dynamic_cast. I don't code that way, nor do any of the libraries I
use.

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