Question

I have a block of code that should be evaluated again at run-time if needed.

class Test

    def initialize
        @some_block = nil
    end

    def make_initial_attributes(&block)
       # do stuff with the supplied block, and then store the block somewhere
       # for later
    end

    def rebuild_attributes
       # grab that stored block and evaluate it again
    end 
end

I have Test objects that are created at start-up, but then throughout the program, I may want them to “update” themselves by running whatever block I fed them with way back at start-up.

Maybe the state of the program has changed and so these Test objects will happily check a bunch of things and let them determine what to update their values with. Of course, the block is something I write so (I think) they shouldn’t be able to do things that I didn’t plan…

The example is a little strange. Basically is it possible to store a block of code (which is just a Proc I believe) and then re-evaluate it later.

Answer 1

What you request is exactly what blocks are for. You just use ‘call’ to the stored block. Here is an example:

class Test
    def initialize
        @some_block = nil
    end

    def make_initial_attributes(&block)
      @some_block = block
       # do stuff with the supplied block, and then store the block somewhere
       # for later
    end

    def rebuild_attributes
      @some_block.call(1)
       # grab that stored block and evaluate it again
    end
end

test = Test.new
test.make_initial_attributes do |i|
  puts i
end
test.rebuild_attributes  # 1

test.make_initial_attributes do |i|
  puts i+1
end
test.rebuild_attributes # 2