[boost] [proto] Looong compile times and other issues

Subject: [boost] [proto] Looong compile times and other issues
From: John Maddock (boost.regex_at_[hidden])
Date: 2011-09-11 13:18:49

So.... I thought I had all the expression template stuff pretty much done, 
and then I tried some real world use cases (compiling all the students_t 
distribution functions with my extended-precision FP type) and everything 
fell apart:

* VC10 wouldn't compile the code at all - more or less runs the system out 
of swap space (takes about 10 minutes or more!), then exits with an internal 
compiler error (if I break the code down into it's parts and instantiate 
each part separately it does compile though - that's not a solution 
though!).
* GCC-4.4.x fails to compile the code due to clashes between 
boost::math::complement (a function) and boost::proto::complement (a class). 
I suspect this is an old gcc bug (finding structures via ADL) - I guess the 
solution is to not derive my number type from a proto-type so ADL can't find 
proto:: classes?   Or will I hit this from some other unforeseen lookup?
* GCC-4.5.0 Fails with an internal compiler error :-(
* GCC-4.6.0 Builds the code OK, but takes a long time - though possibly just 
barely acceptable.

I suspect this is a "triple template" problem:

* proto is complex template library.
* my number class is a fairly large/complex template in it's own right.
* the code above gets instantiated from deep within Boost.Math's internals.

Other than using proto::switch in the grammar (which I'm doing already), is 
there anything I can do to reduce the template load on the proto side of 
things?

Otherwise since I'm only using a tiny fraction of proto's capabilities, the 
only other option I can see is to rip it out and replace with a mini-proto 
designed to minimalize template instantiations within this particular use 
case.

Thanks in advance, John.