[boost] [parameter] Compile-time performance

Subject: [boost] [parameter] Compile-time performance
From: Domagoj Saric (domagoj.saric_at_[hidden])
Date: 2011-02-25 07:58:48

I have an in-house framework a part of which is very similar to 
Boost.Parameter so I tried to refactor it to use Boost.Parameter and, 
unfortunately, noticed a big compile-time hit (the project has a very large 
number instantiations of class templates with 'named non-type template 
parameters').
With my code (and MSVC++ 10) build time was ~56 seconds with a maximum 
cl.exe memory allocation size of ~720 MB. After switching to Boost.Parameter 
build time whent to ~2:24 seconds with a maximum cl.exe memory allocation 
size of ~815 MB.

The most likely suspect is the usage of a forward-sequence for parameter 
type storage (argument packs) from which you fetch passed parameters using 
key-based lookup with the value_type<> metafunction. In my code I use an 
associative container (mpl::map) for the task which has a 
'natural'/'efficient' key-based lookup...
To confirm this I minimally changed the Boost.Parameter-based version of my 
code only to use mpl::maps instead of Boost.Parameter ArgumentPacks and 
built time fell to ~58 seconds...(true, this does not have all the 
compile-time check for correct usage and concept validation that 
ParameterSpecs and ArgumentPacks have but I'd expect this to have a much 
smaller effect than key-based lookup on a forward sequence)...

Is there an inherent issue that forbids the use of an associative container 
for ArgumentPacks or can this be fixed?

-- 
"What Huxley teaches is that in the age of advanced technology, spiritual
devastation is more likely to come from an enemy with a smiling face than
from one whose countenance exudes suspicion and hate."
Neil Postman