Re: [boost] How to specify Boost headers location properly

Subject: Re: [boost] How to specify Boost headers location properly
From: Mateusz Loskot (mateusz_at_[hidden])
Date: 2010-03-11 17:35:24

Vladimir Prus wrote:
> Mateusz Loskot wrote:
>> Steven Watanabe wrote:
>>> Mateusz Loskot wrote:
>>>> For 1st example for the case 1),
>>>> in trunk/libs/accumulators/example/Jamfile.v2, Boost headers are
>>>> located by relative path and mysterious $(BOOST_ROOT)
>>>>
>>>> exe example
>>>>     :
>>>>         main.cpp
>>>>     :
>>>>         <include>../../..
>>>>         <include>$(BOOST_ROOT)
>>>>     ;
>>>>
>>>>   
>>> <include>$(BOOST_ROOT) can be replaced with <dependency>/boost//headers
>>
>> Yet another option I've just learned, but...
>>
>> What is the difference between using headers-only library by specifying
>> this requirement using <source> and <dependency>?
>>
>> The manual says:
>>
>> "(...)a dependency on the target (...) (so it will be brought up-to-date
>> whenever the target being declared is). The dependency is not used in
>> any other way."
>>
>> What does bringing up-to-date mean for headers-only?
>> Also, the "not used in any other way" suggests to me that it does not
>> implicitly update <include> directories.
> 
> Actually, for /boost//headers there's no difference between <source>
> and <dependency>. Every single metatarget in Boost.Build, when built,
> produces two things:
> 
> - actual targets (corresponding to files)
> - set of properties that must be propagated to dependents. These
> are known as usage requirements.

I understand.

> Now, there are three predefined build properties:
> 
> 1. <source> tries to consume the produced targets, and adds usage
> requirements.
> 2. <dependency> sets a dependency on the produced targets, and also adds
> usage requirements.
> 3. <use> only sets usage requirements
> 
> Now, because the 'headers' metatarget never produces any real file, only
> usage requirements, all three are exactly the same.

It makes perfect sense to me now. Great, I think I know how to configure
Boost.Geometry examples and tests now.

Thank you to you and Steven!
-- 
Mateusz Loskot, http://mateusz.loskot.net
Charter Member of OSGeo, http://osgeo.org