Re: Using Boost.Test header-only from CMake

From: Rainer Deyke (rdeyke_at_[hidden])
Date: 2021-06-09 11:05:34

On 08.06.21 09:33, Gavin Lambert via Boost wrote:
> On 8/06/2021 4:53 pm, Edward Diener wrote:
>> I do not know CMake, so maybe my comment is irrelevant, but it seems 
>> natural to me that a header-only library would always choose to use 
>> some other dependent library as header-only, even when that other 
>> library had static or shared variants. In other words I applaud the 
>> decision of Boost.Test to provide a header-only variant and can not 
>> even begin to process the fact that CMake can not deal with Boost.Test 
>> as a header-only library, if that is indeed the case.
> 
> A problem occurs when program P uses library A as static or shared and 
> then wants to use header-only library B which also uses library A.
> 
> For this to work, one of the following must be true:
>  Â  1. library B can figure out how program P chose to link to it and 
> links to it the exact same way.

A header-only library cannot *link* to anything, or it is not header-only.

A header-only library B can depend on symbols being provided by the 
calling program P, which can delegate the task to library A, or to 
another library C which provides the same interface as A.  There should 
be no direct connection from B to A.  Depending on the design of B, this 
may involve #including a header from A before #including a header from 
B, or it can involve making the headers from A available to B so that B 
can #include them directly.  Where these symbols and/or headers come 
from is the business of P, not of B.

-- 
Rainer Deyke (rainerd_at_[hidden])