dynamic nesting of ruby blocks

Question

Imagine i have some resource objects with a run method, which executes the block parameter under the lock held for that resource. For example, like this:

r = Resource("/tmp/foo")
r.run { ... }

How can I write a ruby method which takes an array of resources and executes its block parameter under the lock held for all resources, like:

def using_resources(*res, &block)
  r[0].run do; r[1].run do; r[2].run do ...   

    yield;

  end; end; end; ...
end

Is it possible at all?

Answer 1

You could also do this using #inject:

def using_resources(*resources, &block)
  (resources.inject(block){ |inner,resource| proc { resource.run(&inner) } })[]
end

As you step through the array, you wrap each resource's invocation of the previous Proc in a new Proc, and then pass that to the next resource. This gets the locks in reverse order (the last resource given is the first one unlocked), but that could changed by using resources.reverse.inject ...