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Subject: Re: [Boost-build] [build] Compiler requirement for a header only library
From: Edward Diener (eldiener_at_[hidden])
Date: 2011-04-26 19:25:58

On 4/26/2011 6:40 PM, Matthew Chambers wrote:
> On 4/26/2011 7:03 AM, Vladimir Prus wrote:
>> On Tuesday, April 26, 2011 05:58:47 Dean Michael Berris wrote:
>>> On Tue, Apr 26, 2011 at 8:25 AM, Edward
>>> Diener<eldiener_at_[hidden]> wrote:
>>>> I have a header only library, which needs a particular compiler
>>>> requirement to be set when the library's header files are included.
>>>> I do
>>>> not want to have to change the jam file for every library which uses my
>>>> library. Is there a way to do this with Boost Build so that any library
>>>> which includes one of my library's header files has the particular
>>>> option for the particular compiler set properly. I do know about
>>>> conditional requirements in Boost Build but I do not understand how a
>>>> particular jamfile in a header directory can enforce such an option for
>>>> other libraries.
>>> In your header-only lib you can check for the options used to compile
>>> it -- if it's not there, use #error or #warning to let the user know
>>> what's to be done.
>>> I'm not sure if there's a way to do this in Boost.Build itself,
>>> although it would be awesome if there was a way to do this.
>> While Boost.Build can technically do this, there are two problems:
>> - Each Boost library would have to explicitly list other Boost
>> header-only libraries that it uses
>> - Use code, which might not be using Boost.Build, won't take advantage
>> of this.
>> I don't know how to overcome those issues.
> Pretty much by definition you can't enforce compiler parameters with a
> build system when the object of the enforcement doesn't ever need to be
> built! A header-only library never needs to be mentioned in a Jamfile
> (i.e. even if user code DOES use Boost.Build it likely won't be
> specifying it in Jamfiles).

Certainly a header-only library is a library like any other library,
even if it does not produce a shared or static library. Because of that
it is also a dependency of other libraries which use the header-only
library. Therefore, at least conceptually, there should be a way to say
in a build system that when one uses, ie includes a header file, of a
header-only library, certain usage requirements of the header-only
library should be met which are reflected by changes to the compile
flags of the library using the header-only library.

Perhaps this can be done in Boost Build by specifying the header-only
library as a dependency of other libraries which use the header-only
library, in those other libraries' jamfiles. But I am not sure of the
syntax for such a dependency in Boost Build if it exists.

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