Re: [jamboost] Re: [UI] system libraries

From: Vladimir Prus (ghost_at_[hidden])
Date: 2002-11-26 09:43:04

Markus Schöpflin wrote:

>>2. It differs from using library targets, for no good
>> reason. Moreover, consider that on Windows, a library
>> called 'expat' must be built by Boost.Build, so we
>> have to write
>>
>> exe main : main.cpp : <library>expat
>>
>> But on Linux this library is already awailable, so we better
>> use
>>
>> exe main : main.cpp : <find-library>expat
>>
>> This difference is messy.
> 
> 
> I don't follow you here. Why do have to build 'expat' with boost build 
> on windows? Don't they have a Makefile for this that we better use?

I'd rather not mix two build systems together. But it's
my opinion only.

>>3. I remember that Markus requested that "find-library" had
>> static and dynamic version (i.e "link this system library
>> statically"). But
>>
>> <find-library-static>zlib
> 
> 
> That's what I currently have in my local version of V1.
> 
> 
>> is just too long. An further, if 10 applications use zlib,
>> do they all have to specify it?
> 
> 
> I would say yes. They should specify it.

As I understood you, the linking kind is determined per library basis. I.e
you either link zlib statically in all places, or link it dynamically. Then
specifying this information in all places is redundant, isn't it?

>>So, I propose to
>>
>>1. Kick "find-library". Introduce new "system-lib" target type.
>> For example:
>>
>> system-lib zlib ;
> 
> 
> Why would you need this declaration? To tag on build specifiactions?

So that we know how to interpret

<library>zlib

It's hard to distinguish between using of file called "zlib" and
system library "zlib" otherwise.

>> exe a : a.cpp : <library>zlib ;
>>
>> It's possible to specify static linking
>>
>> system-lib zlib : <shared>false ;
> 
> 
> But this implies that all exe targets in a single Jamfile link to the 
> zlib statically, doesn't it? Not so good, IMO.

Yes, it implies. On the other hand, you can leave

system-lib zlib ;

and then use

exe a : a.cpp : <library>zlib/<shared>false ;

(Not sure this will work now, but that's easy to fix).

> 
> Or would it be possible to say, for example:
> 
> system-lib zlib-dynamic : <shared>true <real-name>zlib ;
> system-lib zlib-static : <shared>false <real-name> zlib ;

Yes, that's an option. Or we could allow "default properties"

system-lib zlib : : default-properties <shared>false ;

By default, this will use static linking, but you can override
it as shown above.

>>2. Kick <library-file> as well. Allow to specify file name as value
>> of <library> features.
>>
>> exe a : a.cpp : <library>zlib <library>helper.a ;
> 
> 
> How do you distinguish between file names and library names? Via 
> presence of system-lib declaration?

Yep. In fact, that's how it works for sources

my_facny_rule a : b ;

Here, if there's main target "b", it will be used. Otherwise,
it's assumed that "b" refers to a file. It's documented in

http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/*checkout*/boost/boost/tools/build/boost_build_v2.html?rev=HEAD&content-type=text/html#target_id

> Hmm, as long as you don't loose the flexibility to specify things 
> individually for each target, I would agree.

Yes, I have another (personal) request for the same ("flexibility to specify
things individually"), so I'll do my best to keep it.

- Volodya