Re: [jamboost] [BB2] Modifiers, some progress towards version support...

From: Rene Rivera (grafik666_at_[hidden])
Date: 2003-02-26 10:43:05

[2003-02-26] David Abrahams wrote:

>Rene Rivera <grafik666_at_[hidden]> writes:
>
>> I made some time to work on the modifier ideas I had. The basic approach
is
>> one borrowed from V1 in which there are modifiers to mutate the
generation
>> of targets, files, etc.
>>
>> I thought I'd post some of the code I have so far, to get some feedback
and
>> to request help. I'm currently stuck because of a current limitation of
BB2.
>> The way the current code works it wraps some basic target types (EXE only
>> for now) with a generic generator that mutates the target. Unfortunately
>> this produces multiple possible transformations for a single target,
which
>> causes an error...
>>
>>
/home/grafik/CVSROOTs/Boost/boost/tools/build/examples-v2/../new/generators.jam:811:
>> in select-dependency-graph from module generators
>> error: 2 possible generations for Can't handle this now.
>>
>> Attached is the code in question. Uncompress while at the BOOST_ROOT.
>>
>
>Somehow I missed the original discussion of this functionality. Is
>the point to be able to define features which change the build
>properties of the target? Or is it to change other aspects of the
>target, like the target filename, which have not been, up till now,
>features in the Boost.Build sense?

Either, the point is to be able to define changes to targets orthagonally to
toolsets. I don't want to write how to name files with a version number for
every toolset, as is the case in V1.

Oh, and there wasn't much original discussion :-)

>The only example I saw was the version modifier; do you have any
>other use-cases?

On other I can immediately think of is to more cleanly, from a user UI
perspective, support adding features like Python module support. That is,
instead of having the $(PYTHON_*) vars like in V1, or the extra target for
module, you can instead have a <python-module> feature with a modifier that
inserts all the needed includes, changes the extension, etc. without having
to touch the toolsets themselves.

Another use case from V1 is the <tag> functionality of stage.

And another from V1, which I'm not sure still applies, is the <template>
functionality. In fact that's the reason I added the modifier concept in the
first place to V1.

I'm sure I'll think of others eventually...

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