dynamic classes and duck typing

[Andrei Alexandrescu]

retard wrote:
> Wed, 02 Dec 2009 16:00:50 -0800, Andrei Alexandrescu wrote:
> 
>> retard wrote:
>>> Wed, 02 Dec 2009 21:16:28 +0000, BCS wrote:
>>>
>>>> Hello Leandro,
>>>>> Again *optimization*. How many times should I say that I agree that D
>>>>> is better than almost every dynamic languages if you need speed?
>>>> I'm not arguing on that point. What I'm arguing is that (at least for
>>>> me) the primary advantages of metaprogramming are static checks (for
>>>> non-perf benefits) and performance. Both of these must be done at
>>>> compile time. Runtime metaprogramming just seems pointless *to me.*
>>> Both the language used to represent D metaprograms and D are suboptimal
>>> for many kinds of DSLs. A dynamic language can provide better control
>>> over these issues without resorting to manual string parsing. If the
>>> DSL is closer to the problem domain, it can have a great effect on
>>> program correctness.
>>>
>>> For instance, you could define natural language like statements in your
>>> DSL with functional composition. In D you basically have to write all
>>> metaprograms inside strings and parse them with CTFE functions. In e.g.
>>> lisp or io the DSL is on the same abstraction level as the main
>>> language. These are of course slow, but in some environments you need
>>> to be able to provide non-developers an intuitive interface for writing
>>> business logic. Even the runtime metaprogramming system can provide
>>> optimizations after the DSL has been processed.
>>>
>>> I understand your logic. It's very simple. You use metaprogramming to
>>> improve performance.
>> Static dimensional analysis doesn't improve performance, and I recall he
>> mentioned that.
> 
> Why not? I agree it does also static checking of type compatibility, but 
> when done at runtime, computing the associated runtime type tag and 
> comparing them also requires cpu cycles. If the analysis is done at 
> compile time, the computational problem degenerates to operations on 
> scalars and types can be erased on runtime if they are not used for 
> anything else.

Doing it at runtime... see Don's VW metaphor. The whole point is to make 
it impossible to write incorrect programs, not to detect those that are 
incorrect. There's a huge difference.

Andrei