Re: [CMake] Can/should we specify optional dependencies

From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2021-10-09 17:11:22

On 10/9/21 6:59 PM, John Maddock via Boost wrote:
> On 08/10/2021 16:10, Peter Dimov via Boost wrote:
>> Andrey Semashev wrote:
>>> Or you could conditionally enable ICU support based on CMake config
>>> option.
>>> We do something like this in Boost.Filesystem:
>>>
>>> https://github.com/boostorg/filesystem/blob/ec93082b6b54cd734b236638e7c4ba76e3b639e7/CMakeLists.txt#L15-L21
>>>
>> The closest example is
>>
>> https://github.com/boostorg/locale/blob/33d06c0c4be7f9bcfb05e200c72f752e9777261c/CMakeLists.txt#L83-L100
>>
>>
> Thanks for the examples everyone, much appreciated.
> 
> I confess I'm having a hard time seeing how a configuration option is
> better than the user simply adding the dependency to their executable
> CMake file?

If you mean ICU dependency then that's exposing Boost.Regex
implementation details (which is what an internal dependency is) to
users. At least, make it a Boost.Regex target for users to depend on.

However, a config option has a configurability advantage. For example, a
user who consumes a product that uses Boost.Regex may choose whether the
whole product will depend on ICU or not. Personally, I would prefer this
kind of flexibility.