Re: [boost] Re: MultiMethod/Visitor Interest

From: Jesse Jones (jesjones_at_[hidden])
Date: 2004-09-29 13:03:34

On Sep 29, 2004, at 3:29 AM, Danil Shopyrin wrote:

> I think about multimethods as about generalized version of virtual 
> method.

Pretty much.

> There are compile time virtual methods in C++, and it's ok. Everyone
> practically use compile time virtual methods. And, by my opinion, the
> generalized version of them also should be compile time. Maybe we speak
> about different things?

Nope, we just have different view points. I see multimethods as 
complementing virtual members instead of  augmenting them. Virtual 
members are fixed at compile time, efficient, type checked, part of a 
class, and special case their first argument. Multimethods are dynamic, 
probably less efficient, largely runtime type checked, not part of a 
class, and treat all of their arguments equally.

The key point is the dynamic bit: one of the weaknesses of C++ is that 
it's quite static: everything is setup at compile time. This is often 
fine, but it does limit flexibility. One of the goals in my multimethod 
library is to add some dynamism to C++ similar to that found in Ruby or 
Smalltalk.
>
>
>
> Maybe there should be at least two versions of multimethods:
>
> 1)       as a generalization of traditional virtual methods;
>
> 2)       as a generalization of "fully runtime polymorphism".
>
Well, what are the advantages to such a scheme? A static library would 
likely be faster, but an optimized dynamic library should be pretty 
fast for common usages as well. Can a static library do better type 
checking? In particular can it figure out, at compile time, if there 
are no applicable methods or no unambiguous method?

   -- Jesse