Supporting multiple versions of an API

Any recommendations on the management of API versions. I have a case in
which it is important that my library support all versions.

For example, currently I am basically doing:

module MyLib
module V0
module Main

end
end

class Main
  def initialize(version)
    extend MyLib.const_get("V#{version}")::Main
  end
end

end

Does that seem like a good approach. Or is it overkill? Is there a
better
way to handle this?

Thanks.

On 31 July 2012 07:54, Intransition [email protected] wrote:

end

Thanks.

For what it’s worth, I kind of like this solution, but I get the
feeling there’s something not quite right about it. An alternative
could be to strategically name source files, and require the
appropriate one; in that case each version-specific file could
redefine the relevant part of Main. E.g.

File: main.rb

class Main
def initialize version
require “./main-v#{version}.rb”
end
# universal code
end

File main-v0.rb

class Main
# version-specific code
end

It splits things up into maintainable files quite nicely, and also has
less parsing (for what that’s worth.) However it wouldn’t work if you
need two different versions of Main in the one program.

Alternatively you could create a factory, which is essentially what
you’ve done, but might be a bit more recognisable to, or better
understood by, maintainers. E.g.

class Main
# … universal code
end
class MainV0 < Main
# … version-specific code
end
module MainFactory
def self.create version
const_get(“MainV#{version}”).new
end
end

It’s mostly a fluff change to what you’ve already got, but it means
each object has the version-specific API as their class rather than a
mixed-in module (i.e. no real difference as far as I’m aware), and
it’s clear that the MainFactory is a factory and that each of the
MainVx classes are what it instantiates, whereas a partially
implemented Main class with some strange magic in its #initialize
method might be a bit less clear.

That all said good documentation will almost always trump recognisable
patterns or otherwise self-documenting code.

I’d be interested to see other peoples’ comments.


Matthew K., B.Sc (CompSci) (Hons)
http://matthew.kerwin.net.au/
ABN: 59-013-727-651

“You’ll never find a programming language that frees
you from the burden of clarifying your ideas.” - xkcd

On Monday, July 30, 2012 9:28:04 PM UTC-4, Matthew K. wrote:

For what it’s worth, I kind of like this solution, but I get the
feeling there’s something not quite right about it.

Same here, but it’s probably just b/c its unusual --its not something
you
can really do in any other language but Ruby, that I know of. Granted it
is
not perfectly ideal in that modules don’t “inherit” exactly in the same
way
classed, but that turns out not to be much of an issue in this case. The
whole notion of this was a sort of inverted factory, so the forward
facing
API looks normal, e.g. Main.new, but versioning still occurs under the
hood.

# universal code

Yep. Exactly why that approach does work in my case.

module MainFactory
implemented Main class with some strange magic in its #initialize
method might be a bit less clear.

Yes, that’s the traditional factory approach. I actually would not want
to
use “MainFactory”, as don’t want it to be explicit. But it occurs to me
that I could have redefined Main.new as a factory method and done it
that
way. And the more I think about it the more that seems like a better
approach. It would work well for Main as well as other classes within
it.

On Thu, Aug 2, 2012 at 4:47 PM, Intransition [email protected]
wrote:

Yes, that’s the traditional factory approach. I actually would not want to
use “MainFactory”, as don’t want it to be explicit. But it occurs to me that
I could have redefined Main.new as a factory method and done it that way.
And the more I think about it the more that seems like a better approach. It
would work well for Main as well as other classes within it.

It seems that in your case the caller decides on the version. Is that
correct?

What about this?

file mylib.rb:

module MyLib

manual

autoload :V0 ‘mylib/v0’
autoload :V1 ‘mylib/v1’

generated

%w{V0 V1}.each do |ver|
autoload ver.to_sym “mylib/#{ver.downcase}”
end

the default

Default = V1

to make access to the current version easy:

def self.const_missing©
Default.const_get©
end
end

and in mylib/v0 etc.

module MyLib
module V0
class Main; end
end
end

Usage

current

m = MyLib::Main.new(…)

explicit

m = MyLib::V0::Main.new(…)

The const_missing trick works only if there are no name conflicts, of
course.

Kind regards

robert

On Thursday, August 2, 2012 12:14:27 PM UTC-4, Robert K. wrote:

approach. It

would work well for Main as well as other classes within it.

It seems that in your case the caller decides on the version. Is that
correct?

Yes, but it is actually via YAML file. It will read in, eg.


revision: 1

Then when it does a Main.load on the file, it will look for the
revision field and determine which version of the API to use.

%w{V0 V1}.each do |ver|
end

current

m = MyLib::Main.new(…)

explicit

m = MyLib::V0::Main.new(…)

The const_missing trick works only if there are no name conflicts, of
course.

Adding some convenience, nice. I like autoload too, but word has it, it
is
being deprecated (albeit in the distant future).

On Thu, Aug 2, 2012 at 10:08 PM, Intransition [email protected]
wrote:

I could have redefined Main.new as a factory method and done it that
way.
And the more I think about it the more that seems like a better
approach. It
would work well for Main as well as other classes within it.

It seems that in your case the caller decides on the version. Is that
correct?

Yes, but it is actually via YAML file. It will read in, eg.

Then when it does a Main.load on the file, it will look for the revision
field and determine which version of the API to use.

So it’s not the user deciding on the API version! That’s a
different situation. Or does the user present the loaded YAML file?
Can you be a bit more specific about your usage scenario?

Kind regards

robert

On Thursday, August 2, 2012 5:16:34 PM UTC-4, Robert K. wrote:

So it’s not the user deciding on the API version! That’s a
different situation. Or does the user present the loaded YAML file?
Can you be a bit more specific about your usage scenario?

Well ultimately the user creates the files, in some fashion or another.
So
it just depends on how you look at it, I guess.

I’ll put a link to the project once it’s a bit more settled. Right now
the
project is in the demonic throws of the Over-Thought.

On Thursday, August 2, 2012 10:47:19 AM UTC-4, Intransition wrote:

It splits things up into maintainable files quite nicely, and also has
less parsing (for what that’s worth.) However it wouldn’t work if you
need two different versions of Main in the one program.

Yep. Exactly why that approach does work in my case.

That should be “does not”.

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