Re: [boost] [review] Fast track formal review of Forward library begins today

From: Tobias Schwinger (tschwinger_at_[hidden])
Date: 2007-12-06 15:12:09

Joel,

thanks for this review.

Joel de Guzman wrote:
> John Torjo wrote:
> 
>>      * What is your evaluation of the design?
> 
> simple and effective. I'd like to see more tweakable
> parameters for specific uses. I frequently deal with
> different number expansions in a case to case basis.
> For example, is it possible to have arity 3 for function
> X and arity-5 for function Y? A single number seems
> wasteful if I'm sure that a certain use needs only a few.
> Is that possible?

Yes, I think so. And it turns out to be a very good idea, as it
potentially makes overload resolution *a lot* faster. Here comes the 
benchmark compiling do_the_bind.cpp, ported to use the forward adapter 
with gcc:

   Arity=8
   preprocess

   real    0m1.384s
   user    0m1.270s
   sys     0m0.109s

   preprocess, compile, link

   real    0m12.405s
   user    0m11.769s
   sys     0m0.540s

   Arity=4
   preprocess

   real    0m0.918s
   user    0m0.454s
   sys     0m0.081s

   preprocess, compile, link

   real    0m1.949s
   user    0m1.653s
   sys     0m0.268s

Interestingly preprocessing is a minor concern and so we could even 
provide means to take our pick at compile time (as opposed to 
preprocessing time).

>>      * What is your evaluation of the implementation?
> 
> again, simple and effective.
> 
>>      * What is your evaluation of the documentation?
> 
> concise and sufficient for its purpose. I'd like to see
> more information on result type deduction though. It says:
> "Boost.ResultOf  can be used to determine the result
> types of specific call expressions.". Ok, but what does
> that really imply? It would be good to have some information
> on this and its implications. For instance, for polymorphic
> function objects, do we have to supply all the nested /result/
> metafunction for all overloads? 

I see. This question really shouldn't be left unanswered.

> How can the forward_adapter template know what to return? 

"By applying result_of" - anything beyond that should probably be said
within the docs of ResultOf...

> I'd like to see an example for a polymorphic function.

...which also might be the more appropriate place for such an example.

Slightly slipping off topic, I wonder whether the docs of ResultOf been 
updated to refer to the current version of the specification (with 
changed semantics for reference types). We should really get this taken 
care of before 1.35 goes out.

Regards,
Tobias