From: Jon Hart <jhart@...>
Date: 2012-01-05T04:42:27+09:00
Subject: Including/selecting modules based on the methods they define

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At http://spoofed.org/go.tar.gz I've put a simplified version of a problem
I haven't yet found a good way to solve.  I'm looking for input as to how
you'd solve the problem.

Basically I have a command line utility that takes three arguments -- an
action, a vendor and a product.   Only three actions (eat, drink, rest) are
supported.  Any number of vendors and products can be added by simply
creating a specially configured plugin.rb in the vendor/product directory.

The issue is that not every vendor product combination will support all
three actions.  When 'go' is run and an action is specified that the given
vendor/product doesn't support, I want to:

1) Handle this gracefully
2) Show all vendors + products that support this action

go is as simple as:

#!/usr/bin/env ruby

unless (ARGV.size == 3)
    raise "Usage: $0 <action> <vendor> <product>"
end

(action, vendor, product) = ARGV

require File.join("plugins", vendor, product, "plugin.rb")

case action
when /eat/
    eat
when /rest/
    rest
when /drink/
    drink
else
    raise "Unknown action #{action}"
end

And a given vendor + product, say Foo Bar, which lives in
plugins/foo/bar/plugin.rb contains:

module Go
    module Foo
        module Bar
            def eat
                puts "Foo::Bar eat!"
            end
            def rest
                puts "Foo::Bar rest!"
            end
        end
    end
end
include Go::Foo::Bar


Another vendor + product, Blaf Blarg is similarly implemented, but supports
all three methods.

As it stands today, if you specify an action that the vendor product does
not support (for example Foo::Bar.drink), an exception is thrown.  Again, I
want to handle that more gracefully (which is easy enough with
begin/rescue) and then show all the vendor products that do support drink.

I feel like the answer lies somewhere around responds_to?, however I'd need
to have access to the module name to call responds_to?, and as currently
implemented this code doesn't know the module name.

Any feedback would be appreciated!

Thanks,

-jon

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