Asp Forum - Gem Dependancies

James Gray

5/22/2005 5:28:00 PM

With HighLine, we've recently moved over to using termios... on Unix
only. I set it up as a gem dependancy and this is causing problems
with the Window's install (and we don't even need it on that
platform). That leads me to the following questions:

1. Is it possible to change dependancies based on the platform?
2. Will a gem install still if you say no to a dependancy?
3. What is The Ruby Way to handle these kinds of install issues?

Thanks for any advice.

James Edward Gray II

6 Answers

Jim Weirich

5/23/2005 12:13:00 AM

On Sunday 22 May 2005 01:27 pm, James Edward Gray II wrote:
> With HighLine, we've recently moved over to using termios... on Unix
> only. I set it up as a gem dependancy and this is causing problems
> with the Window's install (and we don't even need it on that
> platform). That leads me to the following questions:
>
> 1. Is it possible to change dependancies based on the platform?

Not within a single gem. You could provide separate gems with different
dependencies.

> 2. Will a gem install still if you say no to a dependancy?

No. But you can say: gem install highline --ignore-dependencies

--
-- Jim Weirich jim@weirichhouse.org http://onest...
-----------------------------------------------------------------
"Beware of bugs in the above code; I have only proved it correct,
not tried it." -- Donald Knuth (in a memo to Peter van Emde Boas)

James Gray

5/23/2005 1:24:00 AM

On May 22, 2005, at 7:12 PM, Jim Weirich wrote:

> On Sunday 22 May 2005 01:27 pm, James Edward Gray II wrote:
>
>> With HighLine, we've recently moved over to using termios... on Unix
>> only. I set it up as a gem dependancy and this is causing problems
>> with the Window's install (and we don't even need it on that
>> platform). That leads me to the following questions:
>>
>> 1. Is it possible to change dependancies based on the platform?
>>
>
> Not within a single gem. You could provide separate gems with
> different
> dependencies.

Do a few projects do this? Can you point me toward an example project?

Is this on the RubyGems feature request list? If not, can I put it
there? :)

Thanks.

James Edward Gray II

Jeremy Hinegardner

5/23/2005 3:12:00 AM

On Mon, May 23, 2005 at 10:24:27AM +0900, James Edward Gray II wrote:
> On May 22, 2005, at 7:12 PM, Jim Weirich wrote:
>
> >On Sunday 22 May 2005 01:27 pm, James Edward Gray II wrote:
> >
> >>With HighLine, we've recently moved over to using termios... on Unix
> >>only. I set it up as a gem dependancy and this is causing problems
> >>with the Window's install (and we don't even need it on that
> >>platform). That leads me to the following questions:
> >>
> >>1. Is it possible to change dependancies based on the platform?
> >>
> >
> >Not within a single gem. You could provide separate gems with
> >different
> >dependencies.
>
> Do a few projects do this? Can you point me toward an example project?
>
> Is this on the RubyGems feature request list? If not, can I put it
> there? :)

I'll add to it too...

I'm looking at a need for 'optional' dependencies. That is, given a
list of dependencies, at least one of them must be installed for the gem
to work.

Possibly something like:

spec = Gem::Specification.new do |s|
s.add_optional_dependency('SampleGem','>= 0.42.0')
s.add_optional_dependency('OptionalGem','>= 0.10.2')
end

Then during the gem install phase rubygems would check and make sure
that either SampleGem or OptionalGem were installed. If neither were
then prompt to see which one the user would like to have installed. Or
possibly make one of the optional dependencies the default if neither is
installed.

Thoughts anyone ?

enjoy,

-jeremy

--
========================================================================
Jeremy Hinegardner jeremy@hinegardner.org

gabriele renzi

5/23/2005 7:10:00 AM

Jeremy Hinegardner ha scritto:
> On Mon, May 23, 2005 at 10:24:27AM +0900, James Edward Gray II wrote:
>
>>On May 22, 2005, at 7:12 PM, Jim Weirich wrote:
>>
>>
>>>On Sunday 22 May 2005 01:27 pm, James Edward Gray II wrote:
>>>
>>>
>>>>With HighLine, we've recently moved over to using termios... on Unix
>>>>only. I set it up as a gem dependancy and this is causing problems
>>>>with the Window's install (and we don't even need it on that
>>>>platform). That leads me to the following questions:
>>>>
>>>>1. Is it possible to change dependancies based on the platform?
>>>>
>>>
>>>Not within a single gem. You could provide separate gems with
>>>different
>>>dependencies.
>>
>>Do a few projects do this? Can you point me toward an example project?
>>
>>Is this on the RubyGems feature request list? If not, can I put it
>>there? :)
>
>
> I'll add to it too...
>
> I'm looking at a need for 'optional' dependencies. That is, given a
> list of dependencies, at least one of them must be installed for the gem
> to work.
<snip>

I think this are called "virtual" more than optional.
I definitely agree this is needed, but I also see the need for
"optional" gems (which AFAICT are not there, though I may be wrong).
Say, actioncontroller has an utility method that rely on RedCloth.

Putting the whole RedCloth as a dependency would be an overkill, but
telling the user they *could* cooperate would be needed imho.

Jim Weirich

5/24/2005 1:21:00 AM

On Sunday 22 May 2005 11:11 pm, Jeremy Hinegardner wrote:
> I'm looking at a need for 'optional' dependencies. That is, given a
> list of dependencies, at least one of them must be installed for the gem
> to work.
>
> Possibly something like:
>
> spec = Gem::Specification.new do |s|
> s.add_optional_dependency('SampleGem','>= 0.42.0')
> s.add_optional_dependency('OptionalGem','>= 0.10.2')
> end
>
> Then during the gem install phase rubygems would check and make sure
> that either SampleGem or OptionalGem were installed. If neither were
> then prompt to see which one the user would like to have installed. Or
> possibly make one of the optional dependencies the default if neither is
> installed.
>
> Thoughts anyone ?

The problem is that once you get beyond simple dependencies, the requirements
could become quite complicated. Satisfying a simple one out of a set of
optional gems is only the start. The next person might need either gem A or
gems B and C. Someone else needs Gem X on platform Y but Gem W on other
platforms. What one really needs is a full constraint language to handle the
arbitrary combinations.

--
-- Jim Weirich jim@weirichhouse.org http://onest...
-----------------------------------------------------------------
"Beware of bugs in the above code; I have only proved it correct,
not tried it." -- Donald Knuth (in a memo to Peter van Emde Boas)

Aleksi

6/11/2005 9:28:00 AM

Jim Weirich wrote:
> On Sunday 22 May 2005 11:11 pm, Jeremy Hinegardner wrote:
>
>>Possibly something like:
>>
>> spec = Gem::Specification.new do |s|
>> s.add_optional_dependency('SampleGem','>= 0.42.0')
>> s.add_optional_dependency('OptionalGem','>= 0.10.2')
>> end
>>
>>Then during the gem install phase rubygems would check and make sure
>>that either SampleGem or OptionalGem were installed. If neither were
>>Thoughts anyone ?
>
> The problem is that once you get beyond simple dependencies, the requirements
> could become quite complicated. What one really needs is a full constraint
> language to handle the arbitrary combinations.

Jim, I don't want to make this sound simpler than it is, but I'd guess
we have quite good turing complete constraint language at our disposal,
namely Ruby.

> The next person might need either gem A or gems B and C.

if s.gem('A').available?
s.add_dependency('A', '>= 0.42.0')
else
s.add_dependency('B', '>= 0.42.0')
s.add_dependency('C', '>= 0.42.0')
end

> Someone else needs Gem X on platform Y but Gem W on
> other platforms.

if s.platform == "Y"
s.add_dependency("X")
else
s.add_dependency("W")
end

I'm sure we all agree that dependency logic can get complicated, but
then it's time to start simplifying. And if that's not possible, I'm
sure someone writes dependency logic resolver in prolog, or at least
provides yet another dependency to one :).

- Aleksi

comp.lang.ruby

Gem Dependancies

James Gray

Jim Weirich

James Gray

Jeremy Hinegardner

gabriele renzi

Jim Weirich

Aleksi

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