Composable Retriable in Ruby

retriable_example.rb

def attempt_to_deliver
  rand(10) > 8
end

class Deliverable
  def deliver
    if attempt_to_deliver
      puts "Delivered"
      true
    else
      false
    end
  end

  def detour
    puts "Could not deliver. Taking a detour."
  end
end

class Retriable
  def initialize(retriable, attempt_method, failure_method, conditions)
    self.class.class_eval do
      define_method(attempt_method) {
        puts "Trying to perform #{attempt_method} on #{retriable}"
        puts "Checking exit conditions."
        if check(conditions).any? { |condition| condition }
          puts "Some exit condition was true. Calling some failure callback."
          retriable.send(failure_method)
        else
          puts "No exit conditions evaluated to true."
          puts "Trying to do something that might fail."
          if retriable.send(attempt_method)
            puts "It worked. We can stop trying."
          else
            puts "It didn't work. We're trying again."
            send(attempt_method)
          end
        end
      }
    end
  end

  def check(conditions)
    conditions.map do |condition|
      result = condition[:predicate].call(*condition[:args])
      condition[:after].call(condition)
      result
    end
  end
end

conditions = [
  {
    args: [0, 5],
    predicate: -> (attempt, max_attempts) { attempt > max_attempts },
    after: -> (condition) { condition[:args][0] += 1 }
  }
]

deliverable = Deliverable.new
retriable_delivery = Retriable.new(deliverable, :deliver, :detour, conditions)
puts retriable_delivery.deliver

```
~$ ruby scratch.rb
Trying to perform deliver on #<Deliverable:0x007f91ea184128>
Checking exit conditions.
No exit conditions evaluated to true.
Trying to do something that might fail.
It didn't work. We're trying again.
Trying to perform deliver on #<Deliverable:0x007f91ea184128>
Checking exit conditions.
No exit conditions evaluated to true.
Trying to do something that might fail.
It didn't work. We're trying again.
Trying to perform deliver on #<Deliverable:0x007f91ea184128>
Checking exit conditions.
No exit conditions evaluated to true.
Trying to do something that might fail.
Delivered
It worked. We can stop trying.
```