Re: [Boost-build] Extension style

Subject: Re: [Boost-build] Extension style
From: Vladimir Prus (ghost_at_[hidden])
Date: 2010-07-26 08:22:02

On Tuesday 20 July 2010 20:04:11 Vladimir Prus wrote:

> 
> I've managed to implement first-ever Boost.Build extension in Python,
> which exposed some design inconsistency. Here's a relevant bit:
> 
> 
> 	import b2.build.generators as generators
> 
> 	generators.register_standard("verbatim.inline-file",
>     	                         ["VERBATIM"], ["CPP"])
> 
> 	from b2.manager import get_manager
> 
> 	get_manager().engine().register_action("verbatim.inline-file",
> 	"""
> 	./inline_file.py $(<) $(>)
> 	""")
> 
> As you see, 'generators.register_standard' directly registers generators
> in some global table. However, for registering action we explicitly grab
> some global data. I have few questions:
> 
> 1. The straight-forward design is where each module has a set of global
> variables that keep its state. For example, the 'generators' module
> has a list of generators. An alternative design is having a top-level
> "manager" object, which keeps other objects that keep the build system
> state -- like list of features, list of generators and so on. Then,
> most methods will be passed thos individual objects, or the manager.
> The advantage of this design is that in theory, one can load and build
> several independent projects -- which is good for IDE integration, for
> example. However, coding will become much more inconvenient.
> 
> Any comments on what we should prefer? Also, maybe Python allows to
> create several instance of the interpreter, in which an IDE would
> do just that?
> 
> 2. Does that 'get_manager().engine()' thing look horrible, or very horrible?
> 
> 3. Suppose we use 'module.do_whatever' style everywhere. Are there any
> tricks to easily update this to 'manager object' style?

FWIW, this is probably the most important design question for the Python port.

I guess I can try to put it in a different way:

1. Is there a way for a single C++ application to create several, fully
independent, instances of Python interpreter?

2. It is possible, within a single instance of Python interpreter, to
load the same module twice, so and get two copies of global data of
that module?

Thanks,

--
Vladimir Prus
http://vladimir_prus.blogspot.com
Boost.Build: http://boost.org/boost-build2