Re: [Boost-build] ** Need input on alternative selection **

From: Johan Nilsson (r.johan.nilsson_at_[hidden])
Date: 2007-04-24 01:45:54

David Abrahams wrote:
> on Fri Apr 20 2007, "Johan Nilsson" <r.johan.nilsson-AT-gmail.com>
> wrote:
>
>> David Abrahams wrote:
>>> on Tue Apr 17 2007, "Johan Nilsson" <r.johan.nilsson-AT-gmail.com>
>>> wrote:
>>>

[snip]

>>>> - "Details on proposed semantics":
>>>>
>>>> Sounds reasonable, but what about requirements specified for the
>>>> project at a higher-level Jamfile?
>>>> Shouldn't these also be considered explicit, or at
>>>> least higher ranked than the defaults?
>>>
>>> I don't understand.  Example, please?
>>
>> prompt> bjam debug-symbols=on
>>
>> ~=
>>
>> project foo :   requirements <debug-symbols>on ;
>> +
>> prompt> bjam
>
> Sorry, I still can't understand what that is supposed to mean.  What
> are "~=" and "+" doing there?
>

I meant that the combination of the latter two items is roughly equivalent 
to the former bjam invocation, in terms of later target selection. Sorry, 
that's the best explanation I can give right now.

>>>> Just throwing out an idea off the top of my head: What about
>>>> ranking the properties from e.g. high-to-low: explicit
>>>> (command-line) => explicit (project requirements) => explicit
>>>> (target requirements) => implicit (default)? Don't know if that
>>>> would make sense, though.
>>>
>>> Sounds complicated.  Is it driven by a real use-case?
>>>
>>
>> As I said - "off the top of my head". It would probably be complex to
>> implement. Also, I suppose that target requirements should be ranked
>> higher than project requirements. See previous comment about project
>> requirements, though.
>
> I don't believe that it's appropriate to add complexity without real
> use cases (and sufficiently important ones) to justify it.

Well, I guess I'll have to agree.

/ Johan