Ruby block scope - how to call instance method

Question

I'm having a bit of trouble with a block in Ruby. I've created a class which monitors a directory using the fssm gem. When a change occurs I want to notify observers. I'm using the Observable module.

Code:

require 'fssm'
require 'observer'

class FSSM_Spike
include Observable

def initialize watcher
    add_observer watcher
    FSSM.monitor('./temp/', '**/*', :directories => true) do
        update do |base, relative|
            puts 'update'
            notify_observers(self, 'update')
        end
        delete do |base, relative|
            puts 'delete'
            notify_observers(self, 'delete')
        end
        create do |base, relative|
            puts 'create'
            notify_observers(self, 'create')
        end
    end
end
end

Any observers which want to create an instance of FSSM_Spike must pass themselve to new. These then get added to the list observers. However, when a FSSM callback occurs, the method notifiy_observers is not known, as self in that context is FSSM::Path.

I tried adding another method to FSSM_Spike to see if I could call that but had the same result.

How can I call methods from within a block context?

Where is `notify_observers` method defined? – Agis Jan 28 '14 at 13:41 — Agis, Jan 28 '14 at 13:41
It's part of the Observable module – barry Jan 28 '14 at 14:50 — barry, Jan 28 '14 at 14:50

score 2 · Accepted Answer · answered Jan 28 '14 at 14:02

2

def initialize watcher
  # ⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓
  this_observer = self
  …
  create do |base, relative|
    puts 'create'  # ⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓
    notify_observers(this_observer, 'create')
  end
end

should do the trick if I properly understood what do you want to achieve.

answered Jan 28 '14 at 14:02

Aleksei Matiushkin

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It's just about there: `this_observer.changed this_observer.notify_observers(...)` – barry Jan 28 '14 at 16:00
The `changed` call is necessary for the notification to proceed – barry Jan 28 '14 at 16:01

Agis · Answer 2 · 2014-01-28T15:05:31.733

You can save the current value of self in a variable and pass it later to the block:

require 'fssm'
require 'observer'

class FSSM_Spike
include Observable

def initialize watcher
    current_object = self # save reference to the current object

    add_observer watcher
    FSSM.monitor('./temp/', '**/*', :directories => true) do
        update do |base, relative|
            puts 'update'
            current_object.notify_observers(current_object, 'update')
        end
        delete do |base, relative|
            puts 'delete'
            current_object.notify_observers(current_object, 'delete')
        end
        create do |base, relative|
            puts 'create'
            current_object.notify_observers(current_object, 'create')
        end
    end
end
end

Ruby block scope - how to call instance method

2 Answers2