Ruby Callback System

Question

I need a way to store and retrieve callbacks in Ruby, so I made a Callbacks class. Any suggestions would be greatly appreciated.

class Callbacks
 def initialize
 # name: name of callback
 # event: event of which it belongs
 # callback: block to call
 @callbacks = []
 end
 def add name, event, &block
 if block_given?
 @callbacks << {
 name: name,
 event: event,
 callback: block
 }
 end
 end
 def get options={}
 name = options[:name]
 event = options[:event]
 @callbacks.each do |h|
 if name and event
 return h if h[:name] == name and h[:event] == event
 else
 return h if h[:name] == name or h[:event] == event
 end
 end
 nil
 end
end

• Rahul Gopinath: Just to be sure, you are returning the callback even if one of the properties does not match. Is this intensional?
• user12400: Yes, it is returning a callback even if one of the options is not defined.
• Rahul Gopinath: In your code, it would match even if both the options are defined but say the name does not match. Surely this is not the correct behavior then?
• user12400: That doesn't sound right. If :name and :event are defined, it searches for a callback that matches both :name and :event. Otherwise, it matches one or the other.
• Rahul Gopinath: Oh ok, my mistake.

Answer 1

Why not use a hashmap as the main DS? That way, you optimize for when name and event are defined, and suffer only a constant penalty and degrades to linear for other cases. (In your solution the cost is always linear). (As below)

class Callbacks
 def initialize
 @callbacks = {}
 end
 def add(name, event, &block)
 key = {:name => name, :event => event}
 @callbacks[key] = block if block_given?

shouldn't we throw an exception if block is not given?

 end
 def get(o={})

We can use values_at to extract multiple values from a hash.

 name,event = o.values_at(:name,:event)

We don't need to check if name and event separately because equality checking does it for us.

 return @callbacks[o] if name and event
 @callbacks.each do |k,v|
 return v if k[:name] == name or k[:event] == event
 end
 nil
 end
end

And shouldn't you provide a way to unregister from callback?