KatPadi's Point

Handling Errors Gracefully

Sometimes it makes sense to treat errors as part of an application’s “valid” flow of events. Meaning, expected errors should not necessarily make your code go crazy when random errors are raised.

With that in mind, I created a way to implement some kind of “Result Object” by rescuing StandardError instances and handling these errors gracefully.

class Gracefully
  class << self
    alias_method :handle, :new
  end

  attr_reader :error, :value

  def initialize
    @value = nil
    @error = nil
    begin
      @value = yield
    rescue => e
      @error = e
    end
  end

  def success?
    error.nil?
  end

  def on_success
    return self unless success?
    result = yield(@value)
    return result if result.is_a?(Gracefully)
    Gracefully.handle { result }
  end

  def on_failure
    return self if success?
    result = yield(@error)
    return result if result.is_a?(Gracefully)
    Gracefully.handle { result }
  end
end

Gracefully is a wrapper for a result object that will either be a success value or an error object, depending on the block that was passed and invoked.

result = Gracefully.handle { Order.find 999 }

In the example above, if order with id 999 does not exist, result.success? method will return false. Otherwise, true.

If result.success? is true, result.value will contain the successful value. Otherwise, result.error will hold the error object itself.

Whenever Gracefully.handle is called, it will return a Gracefully object. If you want to get the raw value, you can use result.value.

More Usage

result = Gracefully.handle { ComplicatedService.new(foo, bar).process }
if result.success?
  # do success stuff
  use_value(result.value)
else
  # do failure stuff
  log_error(result.error)
end

Chaining Usage

Gracefully.handle { SomeComplicatedService.new.call }.on_success do |val|
  val.update!(column_name: 'stuff')
end


Gracefully.handle { SomeComplicatedService.new.call }.on_failure do |e|
  do_whatever_you_wish_with_the_error(e)
end

By using this, I can be resilient in handling errors. This will help me recover from failures in the process flow.

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